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Re: Null Object Pattern

by Richard O'Keefe

Never forget that the Proxy pattern was developed in the context of a TYPED programming language. So "Clients can't tell whether they work with a subject or its proxyâ means WITH REFERENCE TO A STATED PROTOCOL. Doing this in Ada or Java is fine, because you define an interface type, and that makes it safe. Here is a sentence from a typical description of the pattern: "Since the proxy implements the INTERFACE as the original class, it can be passed to any client that expects a real service object." Having a specified and *enforced* smallish interface prevents the maintenance issues that plague attempts to use this pattern in Smalltalk. Remote objects and local objects have different semantics because remote messages and local messages have different semantics. Local messages cannot be lost, duplicated, or reordered, nor can communication with a local object drop out for no local reason. Version skew is a much bigger problem with distributed systems than local ones, so once again, it is proxying WITH REFERENCE TO A STATED PROTOCOL (and that not a large one!) that counts. There is no such thing as a 100% transparent remote proxy. So it is very useful to know what an object really is as well as what it pretends to be. That is, #class #apparentClass #isNil #apparentlyNil are *different*, So the argument thus far is - a selector should not be inlined if it might need to be overridden - such as in an application of the Proxy pattern - but well-designed Proxies are such WITH REFERENCE TO STATED PROTOCOLS - meaning that selectors that are NOT in such protocols are fair game for inlining.

March 20, 2022

Re: Null Object Pattern

by James Foster

Hello Richard, > What part of â¦ is hard to understand? Did you mean for this to come off as condescending? Or are you are honestly wondering how effectively you are communicating? In either case, all of it is hard for me to understand since it doesnât describe the Proxy Pattern which requires that "Clients can't tell whether they work with a subject or its proxyâ (https://en.wikipedia.org/wiki/Proxy_pattern <https://en.wikipedia.org/wiki/Proxy_pattern>). My understanding of a proxy is that it will rarely/never happen that "there will be *more* selectors you needed to think about but didnât." So, far from being (an instance of) the problem, an override of #âdoesNotUnderstand:â is the elegant solution. > I wanted something that was like an OrderedCollection but could only hold elements of a specific class. It seems what you want is not a Proxy but a Facade (https://en.wikipedia.org/wiki/Facade_pattern <https://en.wikipedia.org/wiki/Facade_pattern>) in which you "may perform additional functionality [such as type checking] before ... forwarding a requestâ (https://en.wikipedia.org/wiki/Facade_pattern <https://en.wikipedia.org/wiki/Facade_pattern>). > I *could* make a proxy by going through #doesNotUnderstand: but I am not going to. Thatâs fine, and a proxy is probably inappropriate for the things you do. But there are a few usage scenarios <https://en.wikipedia.org/wiki/Proxy_pattern#Possible_usage_scenarios> where they are appropriate. My primary experience with them is with distributed object communication <https://en.wikipedia.org/wiki/Distributed_object_communication> where they are appropriate. > I *could* make a batch of ricin and store it in my granddaughter's bedroom, but I'm not going to. Iâm glad to hear it. To take a more realistic example, I could try to fly a 747 but Iâm not going to (since my commercial pilotâs license doesnât include that rating). That doesnât mean that no one should fly a 747 (or implement a Proxyâthe people who make GemBuilder for Smalltalk <https://gemtalksystems.com/products/gbs-vw/> should certainly use proxies). I remember hearing a joke about Kent Beck holding a sign saying âWill override #doesNotUnderstand: for foodâ! I took it as not saying that only a genius can understand DNU but that you should think carefully about how it will be used (and in many cases something else would be appropriate). Everything else about Kent Beckâs work makes it clear that leaving behind clear maintainable code is a top priority. James > On Mar 19, 2022, at 11:11 PM, Richard O'Keefe <raoknz(a)gmail.com> wrote: > > An override of #doesNotUnderstand: *is* (an instance of) the problem. > What part of "you may think you know what to forward now, but just > wait a couple of months or install an additional package and there > will be *more* selectors you needed to think about but didn't" is > hard to understand? > > Proxies done right are proxies *relative to a specified protocol*. > > Let me give you a personal example. > I wanted something that was like an OrderedCollection but > could only hold elements of a specific class. > No worries, just make a proxy. Make a bare-bones object, > define all the #add... methods to check their argument, > and use #doesNotUnderstand to forward everything else to > the underlying OrderedCollection. > > The first problem is the selectors that the bare-bones > object *does* understand by virtue of being an object. > (Remember there are *hundreds* of these selectors in > Squeak, Pharo, VisualWorks, even in gst there are more > than 120). You must, for example, ensure that #instVarAt: > is forwarded, not handled locally, BUT you must also > ensure that #instVarAt:put: is handled locally, not forwarded. > And then one day you find that your program has broken, > because mutable collections now have > aMutableCollection inPlaceCollect: collectBlock > and that can put unacceptable results in the collection > *without* going through any #add... method. > > Eventually you realise "handing out a wrapper for this > collection constrained to only allow adding certain things" > is the wrong way to do it, and you do something like > > constrainedAdder: constraint > ^[:x | (constraint value: x) > ifTrue: [self add: x] > ifFalse: [DomainError receiver: self selector: #add:]] > > or you do something else entirely, like handing out a wrapper with > a *narrow* interface that doesn't make the slightest pretence of > *being* the other object. > > I *could* make a batch of ricin and store it in my > granddaughter's bedroom, but I'm not going to. > I *could* make a proxy by going through #doesNotUnderstand: > but I am not going to. That would be a textbook example of > maxim 38: "Just because it's easy for you doesn't mean it > can't be hard on your clients." > > > > > > > On Sun, 20 Mar 2022 at 15:18, James Foster <smalltalk(a)jgfoster.net <mailto:smalltalk@jgfoster.net>> wrote: > I donât understand. Wouldnât an override of #'doesNotUnderstand:â solve this problem? The proxies Iâve seen subclass from nil or ProtoObject and forward almost everything to the target. Itâs really very easy. > >> On Mar 19, 2022, at 3:14 AM, Richard O'Keefe <raoknz(a)gmail.com <mailto:raoknz@gmail.com>> wrote: >> >> An object should be a Proxy or Stub only with reference to a specific protocol, which should be kept narrow. >> >> Being a Proxy is a form of coupling. Proxying a wide >> interface creates maintenance problems: >> Squeak 5.3 : Object selectors size => 485 >> Pharo 9.0 : Object selectors size => 435 >> astc : Object selectors size => 325 >> VW 8.3PUL : Object selectors size => 304 >> >> The interface of Object is HUGE. You want to bet that >> your Proxy got *all* of the methods right? This >> interface didn't get that way all at once; it grew. >> The number was 78 in Smalltalk-80. At a minimum, then, >> Smalltalk systems have accreted one extra Object method >> every two months. >> >> So you set up your proxy to *flawlesly* mirror Object, >> and then, WHOOPS, upgrade Smalltalk and now there is a >> method that Object has and your Proxy either lacks (if >> it descends from ProtoObject but not Object) or inherits >> an inappropriate version of (if it descends from Object). >> >> What this means is that nobody ever *does* flawlessly >> mock everything in the public interface of an object >> they are Proxying. They proxy a *limited* protocol. >> Because that is all they *can* do. >> >> Look, I know that people who have been trained to work >> with the stuff can use C4 as cooking fuel. But I haven't >> had that training, so I won't touch the stuff. In the >> same way, I dare say there are things *you* can safely >> do in Smalltalk that fumblefingers here would be burnt >> badly by. There are many things that *can* be done that >> I *won't* do. In a chemistry lab, I would not work with >> ClF3 let alone O2F2. In Smalltalk, I don't monkey with >> #isNil. >> >> On Fri, 18 Mar 2022 at 03:52, James Foster <smalltalk(a)jgfoster.net <mailto:smalltalk@jgfoster.net>> wrote: >> Richard, >> >> I very much admire Dijkstraâs admonition regarding âThe Humble Programmerâ and was pointing a student to that article just this week. >> >> In any case, I think youâve demonstrated that you now comprehend the argument against inliningâyou just donât agree. Thatâs fair and I think the discussion has been clarified. Would it be fair to say that you have an âideological objectionâ to allowing a Proxy or Stub to transparently stand in for another object (say, in a two-object-space environment such as Pharo and GemStone)? That is, a domain object canât be replaced by a Proxy or Stub without a wholesale rewrite of the rest of the application? I respect that as a reasonable position (demanding perfect clarity), but I see a cost to that position as well. >> >> Of course, if you really want to avoid allowing the receiver to chose its response to a message, you can use other messages. So if you want to find out if an object is identical to nil you should use `nil == myObject` to ensure that there was not an override of #âisNilâ or #â==â by the objectâs class. >> >> James >> >>> On Mar 17, 2022, at 2:27 AM, Richard O'Keefe <raoknz(a)gmail.com <mailto:raoknz@gmail.com>> wrote: >>> >>> My chief concern is that I am a bear of very little brain, >>> and if you change the meaning of #isNil to anything at all >>> other than "is the receiver identical to nil" you *WILL* >>> (not may) confuse me. This extends to things that happen >>> not to be inlined: if even a god-like Smalltalker like >>> Andres Valloud overloads #, to something other than "combine >>> the collection that is the receiver with the collection that >>> is the argument to yield a new collection" than I *WILL* >>> most certainly be confused and find the code unmaintainable. >>> Smalltalk being Smalltalk, if you admit an inconsistent >>> overload anywhere, I can no longer understand sends of that >>> selector anywhere. One of the things to like about Traits >>> is that you can say "this class doesn't just *happen* to >>> have selectors x and y, it has them *because* it has this >>> whole consistent bundle of selectors." >>> >>> There are more annotations documented for my Smalltalk >>> compiler than are actually implemented. One that *is* >>> implemented is <doNotOverride>, and it has caught more >>> mistakes than I care to admit to. It's particularly >>> important for a bundle of methods with varying arguments >>> that are meant to be routed through a single method, >>> which *is* meant to be overridden. It makes sure that >>> I override the *right* method. (Take #= and #~= as an >>> obvious example.) >>> >>> Once you start down the path of lying about things like #isNil >>> you find that EITHER you have to go very far down that path >>> and override #== and #instVarAt: and a whole lot of other >>> things OR you are working with a semantically incoherent system. >>> >>> "How should a proxy (https://en.wikipedia.org/wiki/Proxy_pattern <https://en.wikipedia.org/wiki/Proxy_pattern>) to nil respond to the #âisNilâ message?" >>> >>> It SHOULD NOT LIE. A proxy *isn't* nil, and it doesn't *behave* like nil, >>> even if it is a proxy for nil. A proxy, qua proxy, can do things that nil >>> cannot. Use another selector, #isEffectivelyNil, or whatever reveals your >>> intentions, and give it what semantics you find useful. >>> >>> "How should the Null Object Pattern (https://en.wikipedia.org/wiki/Null_object_pattern <https://en.wikipedia.org/wiki/Null_object_pattern>) respond to #âisNilâ?" >>> >>> It should answer false. Period. No ifs, buts, quibbles, or maybes. >>> The whole *point* of the Null Object Pattern is to return something >>> that *isn't* nil, that has quite a different protocol. If you call >>> something that is supposed to return either a Foo or a NullFoo, and >>> it gives you nil instead, there is a BUG in what you just called so >>> the sooner you find out the better. What you want is >>> >>> Foo >> isNullFoo ^false >>> NullFoo >> isNullFoo ^true >>> and no other class defines #isNullFoo. >>> >>> That way, when you ask "tripeWorks grobblingMill lastPallet isNullPallet" >>> (a) you make it clear to someone reading your code what you are expecting >>> (b) if you DON'T get what you are expecting, Smalltalk will tell you. >>> >>> I must admit that on the few occasions when I've used Null Object >>> I've used an all-purpose #isMissing instead of a task-appropriate >>> #isNullFoo, but then I figured out what I was doing wrong. You >>> look at the code, you say "there's *something* off here, but I don't >>> know what." But when you ask "what, exactly, does this method MEAN?" >>> you realise "oh, THAT'S what I was doing wrong." #isMissing told me >>> it was a NullPerson or a NullAddress or a NullPartsList or ... but >>> in this case I needed to know whether it was a NullSummary. >>> >>> And of course you run into E.F.Codd's lesson: "one NULL is never >>> enough, information can be missing for more than one reason". >>> Take the familiar example of a phone number: >>> - I know that Fred's phone number is X >>> - I know that Fred has a phone but I don't know what the number is >>> - I don't know whether Fred has a phone or not >>> - I know that Fred has no phone >>> There's room for three *different* null objects there. >>> Should we have UnknownNumberOfActualPhone to answer false to #isnil >>> and NonNumberOfNonexistentPhone to answer true? Or what? >>> >>> By the way, you may have misunderstood my benchmark. >>> It wasn't that #isNil or even _ ifNotNil: speeded up by >>> 10%, it was the *whole* matrix-munching benchmark that >>> speeded up. Certainly not a big deal, but it's not >>> something I'd be happy to give up in order to get less >>> maintainable code. >>> >>> >>> >>> >>> >>> >>> >>> >>> On Thu, 17 Mar 2022 at 18:21, James Foster <smalltalk(a)jgfoster.net <mailto:smalltalk@jgfoster.net>> wrote: >>> Richard, >>> >>> My _concern_ with inlining is that since it is designed to short-circuit dynamic method lookup, it is impossible to call a _different_ implementation. That is, you lose the opportunity to have the _receiver_ decide how to respond to the message. You may think of it as a message, but the caller is deciding how the receiver will respondâwhich largely defeats the purpose and role of it being a message. Yes, at the machine code level you are performing a branch instruction, but when comparing OOP to Procedural Programming we typically make a distinction between âmessagesâ and "procedure calls." The distinction is that the receiver gets to decide how to respond to a message. In C++ this is the distinction between a âvirtual" and "non-virtual" function. By inlining, you are converting the function from a virtual function to a non-virtual function, and this can make a difference (which is why virtual functions exist). >>> >>> How should a proxy (https://en.wikipedia.org/wiki/Proxy_pattern <https://en.wikipedia.org/wiki/Proxy_pattern>) to nil respond to the #âisNilâ message? How should the Null Object Pattern (https://en.wikipedia.org/wiki/Null_object_pattern <https://en.wikipedia.org/wiki/Null_object_pattern>) respond to #âisNilâ? >>> >>> And, yes, Iâm sure you can come up with benchmarks that show a measurable difference, but what is the impact in realistic code? When someone asked about inlining #âyourselfâ in GemStone I believe I measured the performance as taking 2 nanoseconds per call (on a 2012 machine). A 10% speedup would make it 1.8 nanoseconds. Is that worth it? Maybe, maybe not. >>> >>> Note that I described my position as a âconcern,â not an ideological objection. Mostly Iâm giving a rationale for something that doesnât seem to be explained very well for you. I accept that there may be a time for inlining, but I can âcomprehend" another side to the issue. >>> >>> James >>> >>>> On Mar 16, 2022, at 9:42 PM, Richard O'Keefe <raoknz(a)gmail.com <mailto:raoknz@gmail.com>> wrote: >>>> >>>> We're still not on the same page. >>>> You seem to have some ideological objection to inlining that >>>> I am completely failing to comprehend. >>>> Just because a procedure call (message send) is inlined doesn't >>>> in the least mean it *isn't* a procedure call (message send), >>>> just as compiling a procedure call (message send) as a jump >>>> (last-call optimisation) doesn't mean it *isn't* a procedure >>>> call (message send). >>>> By the way, forget about "40 years ago". >>>> I just did an experiment in Pharo 9, and found that >>>> using "_ ifNotNil: " instead of "_ izNil ifFalse: " >>>> -- where izNil is a non-inlined self == nil -- >>>> gave a 10% speedup, in a test code where real work was going >>>> on as well. >>>> As for turning off all inlining, what do you think that would >>>> do to #ifFalse:ifTrue: and its relatives? >>>> >>>> >>>> On Thu, 17 Mar 2022 at 08:34, <sean(a)clipperadams.com <mailto:sean@clipperadams.com>> wrote: >>>> >>>> >>>> To start with, why do you CARE whether a particular method is inlined or not? >>>> >>>> I care because it makes âeverything is a messageâ a lie! And I suspect (no proof and could be wrong) itâs an optimization that only made sense with the hardware constraints of 40+ years ago. Arguing against premature optimization is hardly something I just made up ;-) >>>> >>>> This makes absolutely no sense to me. What makes you think that the combination "_ isNil ifFalse: [_]" will NOT be inlined? >>>> >>>> I may have been unclear. My intent was to communicate: âIâd like to stop ALL* inlining of messages by default if possibleâ >>>> >>>> *or as many as practical >>>> >>>> The thing that rings loud alarm bells for me is there being "long chains" in the first place. >>>> >>>> I agree that it is in general a smell, but long chains was tangential to the intention above >>>> >>>> Can you give an example? >>>> >>>> I donât know if I can think of one thatâs not contrivedâ¦ Wrapping something external? Squeakâs AppleScript support used to mirror the underlying AS, which is pretty much exactly that. >>>> >>>> In my own programming, I've generally found that nils turning up in the middle of a chain indicates a serious design error somewhere. >>>> >>>> Agreed. See smell comment above. >>>> >>> >> >

March 20, 2022

Re: Another question about Spec2 and SpTablePresenter

by Esteban Lorenzano

uh, for some reason my mail client eat the formatting... but you get the idea ;) On Mar 20 2022, at 3:14 pm, Esteban Lorenzano <estebanlm(a)netc.eu> wrote: > Hi, > > well, the incomplete documentation of Spec states clearly that you will be receiving two parameters: > onAcceptEdition: aBlock > "Set the block to execute when cell edition is accepted. > `aBlock` receives two arguments: > - the element of the table (See `SpAbstractListPresenter>>#items:` > - the string entered while editing" > acceptAction := aBlock > > So, when you set beEditable to your column, you can do something like this: > items := { #one -> 'one'. #two -> 'two' }. > table := SpTablePresenter new > addColumn: (SpStringTableColumn title: 'Key' evaluated: #key); > addColumn: (SpStringTableColumn new > title: 'Value'; > evaluated: #value; > beEditable; > onAcceptEdition: [ :item :newValue | item value: newValue ]; > yourself); > items: items; > open. > and then you can edit whatever you want and update your item. > > Now, since this is a mechanism that has not been used a lot yet in morphic backend, I just discovered and fixed a bug (not in editable tables, but that affects it: https://github.com/pharo-spec/Spec/issues/1263) so if you want to actually use the functionality, you will need to wait until is merged (tomorrow). > Esteban > > On Mar 20 2022, at 10:26 am, Mark O'Donoghue <mark.odonoghue.2010(a)gmail.com> wrote: > > Howdy all > > > > > > I am making progress with quite a large application which relies heavily on Spec2 > > ( but Spec2 is such a big learning curve for me â especially given the incomplete documentationâ¦ ð) > > > > I am currently struggling with the following issue: > > I have a SpTablePresenter which shows a collection of domain objects (subclassed from Model). > > The domain object are instances of âAssetâ which is a relatively simple class. > > The table works fine. > > > > Now, I need to be able to update some columns , but I donât think I want to build a separate form for doing classic CRUD operations. > > (There is no need for create or delete functionality â so an in-situ update seems desirableâ¦). > > > > Iâve made a start using SpStringTableColumn >> beEditable and #onAcceptEdition: > > > > But I canât see how to work out what row and column has changed, and how I can update the corresponding Asset instance(s). > > It thought it would be handled using #whenModelChanged: but there are models in many places (and at several levels in the Spec hierarchy)â¦ > > Iâve tried following it all the way down to the adapters and morphs but I canât see how the freshly edited cell interacts with the model or announcements. > > > > (BTW - It doesnât look like the âselected itemâ features are appropriate since you can do edits in other rows regardless of what row is/isnât selected.) > > > > Is there a correct and/or elegant way to detect these cell changes in a SpTablePresenter and apply them to my domain objectsâ¦? > > > > Cheers > > Mark > > > > > > > > > > From: Mark O'Donoghue <mark.odonoghue.2010(a)gmail.com> > > Sent: Sunday, 4 July 2021 5:26 PM > > To: pharo-users(a)lists.pharo.org > > Subject: Question about Spec2 and SpTablePresenter > > > > > > > > > > > > Howdy all > > > > Iâve got stuck trying to manage Tables â over 12 hours now and Iâm out of ideas!. â¹ > > > > Any observations / suggestions are most welcomeâ¦ > > > > Iâve been loading small external files of transactions using NeoCSV into Spec2 tables. > > I am trying to use Fuel to persist the table contents so that my application will re-load the working state from where I finished in the last session. > > (Iâve opted for Fuel as a simple alternative to having to do the whole object relational mapping thing.) > > > > The idea is that transactions (and potentially some manual adjustments) will be processed over time. > > (This is preferable to having to reload all files from the beginning evert time I run the applicationâ¦) > > > > The Spec2 tables have been working well until I tried to persist them. > > I canât seem to fully re-load them to a previously saved state. > > > > For example - I can restore the essential contents of my table in most circumstances using: > > > > restoreObjects > > > > âfilePresenter1 is a SpTablePresenterâ > > > > | objects savedEntry | > > > > objects := CpPersist restoreObjectsFromFileNamed: 'E:\Me\zzzST-Test\demo.fuel'. > > > > recentFileList := objects at: 1. > > currFileFilter := objects at: 2. > > savedEntry := objects at: 3. > > > > self updateFilterButton: currFileFilter. > > > > filteredFileList := self filterFilesUsing: currFileFilter. > > > > filePresenter1 items: filteredFileList. > > > > savedEntry > > ifNotNil: [filePresenter1 selectItem: savedEntry ]. > > > > > > However, if any of the table columns are re-sorted , the re-load operation gets confused and I canât get the saved a saved selected item to become selected again. > > > > (It seems to be confusing the index numbers of the sorted and unsorted lists â even when I match by contents rather than index.) > > (I also created an equality test to ensure equivalent entries are recognised by the #= operation in the list of the underlying model ). > > > > This all works fine - unless I sort a column! > > > > Since this approach was going to be used on several screens Iâd really like to find a solution. > > > > Cheers > > Mark > > Perth, Western Australia

March 20, 2022

Re: Another question about Spec2 and SpTablePresenter

by Esteban Lorenzano

Hi, well, the incomplete documentation of Spec states clearly that you will be receiving two parameters: onAcceptEdition: aBlock "Set the block to execute when cell edition is accepted. `aBlock` receives two arguments: - the element of the table (See `SpAbstractListPresenter>>#items:` - the string entered while editing" acceptAction := aBlock So, when you set beEditable to your column, you can do something like this: items := { #one -> 'one'. #two -> 'two' }. table := SpTablePresenter new addColumn: (SpStringTableColumn title: 'Key' evaluated: #key); addColumn: (SpStringTableColumn new title: 'Value'; evaluated: #value; beEditable; onAcceptEdition: [ :item :newValue | item value: newValue ]; yourself); items: items; open. and then you can edit whatever you want and update your item. Now, since this is a mechanism that has not been used a lot yet in morphic backend, I just discovered and fixed a bug (not in editable tables, but that affects it: https://github.com/pharo-spec/Spec/issues/1263) so if you want to actually use the functionality, you will need to wait until is merged (tomorrow). Esteban On Mar 20 2022, at 10:26 am, Mark O'Donoghue <mark.odonoghue.2010(a)gmail.com> wrote: > Howdy all > > > I am making progress with quite a large application which relies heavily on Spec2 > ( but Spec2 is such a big learning curve for me â especially given the incomplete documentationâ¦ ð) > > I am currently struggling with the following issue: > I have a SpTablePresenter which shows a collection of domain objects (subclassed from Model). > The domain object are instances of âAssetâ which is a relatively simple class. > The table works fine. > > Now, I need to be able to update some columns , but I donât think I want to build a separate form for doing classic CRUD operations. > (There is no need for create or delete functionality â so an in-situ update seems desirableâ¦). > > Iâve made a start using SpStringTableColumn >> beEditable and #onAcceptEdition: > > But I canât see how to work out what row and column has changed, and how I can update the corresponding Asset instance(s). > It thought it would be handled using #whenModelChanged: but there are models in many places (and at several levels in the Spec hierarchy)â¦ > Iâve tried following it all the way down to the adapters and morphs but I canât see how the freshly edited cell interacts with the model or announcements. > > (BTW - It doesnât look like the âselected itemâ features are appropriate since you can do edits in other rows regardless of what row is/isnât selected.) > > Is there a correct and/or elegant way to detect these cell changes in a SpTablePresenter and apply them to my domain objectsâ¦? > > Cheers > Mark > > > > > From: Mark O'Donoghue <mark.odonoghue.2010(a)gmail.com> > Sent: Sunday, 4 July 2021 5:26 PM > To: pharo-users(a)lists.pharo.org > Subject: Question about Spec2 and SpTablePresenter > > > > > > Howdy all > > Iâve got stuck trying to manage Tables â over 12 hours now and Iâm out of ideas!. â¹ > > Any observations / suggestions are most welcomeâ¦ > > Iâve been loading small external files of transactions using NeoCSV into Spec2 tables. > I am trying to use Fuel to persist the table contents so that my application will re-load the working state from where I finished in the last session. > (Iâve opted for Fuel as a simple alternative to having to do the whole object relational mapping thing.) > > The idea is that transactions (and potentially some manual adjustments) will be processed over time. > (This is preferable to having to reload all files from the beginning evert time I run the applicationâ¦) > > The Spec2 tables have been working well until I tried to persist them. > I canât seem to fully re-load them to a previously saved state. > > For example - I can restore the essential contents of my table in most circumstances using: > > restoreObjects > > âfilePresenter1 is a SpTablePresenterâ > > | objects savedEntry | > > objects := CpPersist restoreObjectsFromFileNamed: 'E:\Me\zzzST-Test\demo.fuel'. > > recentFileList := objects at: 1. > currFileFilter := objects at: 2. > savedEntry := objects at: 3. > > self updateFilterButton: currFileFilter. > > filteredFileList := self filterFilesUsing: currFileFilter. > > filePresenter1 items: filteredFileList. > > savedEntry > ifNotNil: [filePresenter1 selectItem: savedEntry ]. > > > However, if any of the table columns are re-sorted , the re-load operation gets confused and I canât get the saved a saved selected item to become selected again. > > (It seems to be confusing the index numbers of the sorted and unsorted lists â even when I match by contents rather than index.) > (I also created an equality test to ensure equivalent entries are recognised by the #= operation in the list of the underlying model ). > > This all works fine - unless I sort a column! > > Since this approach was going to be used on several screens Iâd really like to find a solution. > > Cheers > Mark > Perth, Western Australia

March 20, 2022

Another question about Spec2 and SpTablePresenter

by Mark O'Donoghue

Howdy all I am making progress with quite a large application which relies heavily on Spec2 ( but Spec2 is such a big learning curve for me â especially given the incomplete documentationâ¦ ð) I am currently struggling with the following issue: I have a SpTablePresenter which shows a collection of domain objects (subclassed from Model). The domain object are instances of âAssetâ which is a relatively simple class. The table works fine. Now, I need to be able to update some columns , but I donât think I want to build a separate form for doing classic CRUD operations. (There is no need for create or delete functionality â so an in-situ update seems desirableâ¦). Iâve made a start using SpStringTableColumn >> beEditable and #onAcceptEdition: But I canât see how to work out what row and column has changed, and how I can update the corresponding Asset instance(s). It thought it would be handled using #whenModelChanged: but there are models in many places (and at several levels in the Spec hierarchy)â¦ Iâve tried following it all the way down to the adapters and morphs but I canât see how the freshly edited cell interacts with the model or announcements. (BTW - It doesnât look like the âselected itemâ features are appropriate since you can do edits in other rows regardless of what row is/isnât selected.) Is there a correct and/or elegant way to detect these cell changes in a SpTablePresenter and apply them to my domain objectsâ¦? Cheers Mark From: Mark O'Donoghue <mark.odonoghue.2010(a)gmail.com> Sent: Sunday, 4 July 2021 5:26 PM To: pharo-users(a)lists.pharo.org Subject: Question about Spec2 and SpTablePresenter Howdy all Iâve got stuck trying to manage Tables â over 12 hours now and Iâm out of ideas!. â¹ Any observations / suggestions are most welcomeâ¦ Iâve been loading small external files of transactions using NeoCSV into Spec2 tables. I am trying to use Fuel to persist the table contents so that my application will re-load the working state from where I finished in the last session. (Iâve opted for Fuel as a simple alternative to having to do the whole object relational mapping thing.) The idea is that transactions (and potentially some manual adjustments) will be processed over time. (This is preferable to having to reload all files from the beginning evert time I run the applicationâ¦) The Spec2 tables have been working well until I tried to persist them. I canât seem to fully re-load them to a previously saved state. For example - I can restore the essential contents of my table in most circumstances using: restoreObjects âfilePresenter1 is a SpTablePresenterâ | objects savedEntry | objects := CpPersist restoreObjectsFromFileNamed: 'E:\Me\zzzST-Test\demo.fuel'. recentFileList := objects at: 1. currFileFilter := objects at: 2. savedEntry := objects at: 3. self updateFilterButton: currFileFilter. filteredFileList := self filterFilesUsing: currFileFilter. filePresenter1 items: filteredFileList. savedEntry ifNotNil: [filePresenter1 selectItem: savedEntry ]. However, if any of the table columns are re-sorted , the re-load operation gets confused and I canât get the saved a saved selected item to become selected again. (It seems to be confusing the index numbers of the sorted and unsorted lists â even when I match by contents rather than index.) (I also created an equality test to ensure equivalent entries are recognised by the #= operation in the list of the underlying model ). This all works fine - unless I sort a column! Since this approach was going to be used on several screens Iâd really like to find a solution. Cheers Mark Perth, Western Australia

March 20, 2022

Re: Null Object Pattern

by Richard O'Keefe

An override of #doesNotUnderstand: *is* (an instance of) the problem. What part of "you may think you know what to forward now, but just wait a couple of months or install an additional package and there will be *more* selectors you needed to think about but didn't" is hard to understand? Proxies done right are proxies *relative to a specified protocol*. Let me give you a personal example. I wanted something that was like an OrderedCollection but could only hold elements of a specific class. No worries, just make a proxy. Make a bare-bones object, define all the #add... methods to check their argument, and use #doesNotUnderstand to forward everything else to the underlying OrderedCollection. The first problem is the selectors that the bare-bones object *does* understand by virtue of being an object. (Remember there are *hundreds* of these selectors in Squeak, Pharo, VisualWorks, even in gst there are more than 120). You must, for example, ensure that #instVarAt: is forwarded, not handled locally, BUT you must also ensure that #instVarAt:put: is handled locally, not forwarded. And then one day you find that your program has broken, because mutable collections now have aMutableCollection inPlaceCollect: collectBlock and that can put unacceptable results in the collection *without* going through any #add... method. Eventually you realise "handing out a wrapper for this collection constrained to only allow adding certain things" is the wrong way to do it, and you do something like constrainedAdder: constraint ^[:x | (constraint value: x) ifTrue: [self add: x] ifFalse: [DomainError receiver: self selector: #add:]] or you do something else entirely, like handing out a wrapper with a *narrow* interface that doesn't make the slightest pretence of *being* the other object. I *could* make a batch of ricin and store it in my granddaughter's bedroom, but I'm not going to. I *could* make a proxy by going through #doesNotUnderstand: but I am not going to. That would be a textbook example of maxim 38: "Just because it's easy for you doesn't mean it can't be hard on your clients." On Sun, 20 Mar 2022 at 15:18, James Foster <smalltalk(a)jgfoster.net> wrote: > I donât understand. Wouldnât an override of #'doesNotUnderstand:â solve > this problem? The proxies Iâve seen subclass from nil or ProtoObject and > forward almost everything to the target. Itâs really very easy. > > On Mar 19, 2022, at 3:14 AM, Richard O'Keefe <raoknz(a)gmail.com> wrote: > > An object should be a Proxy or Stub only with reference to a specific > protocol, which should be kept narrow. > > Being a Proxy is a form of coupling. Proxying a wide > interface creates maintenance problems: > Squeak 5.3 : Object selectors size => 485 > Pharo 9.0 : Object selectors size => 435 > astc : Object selectors size => 325 > VW 8.3PUL : Object selectors size => 304 > > The interface of Object is HUGE. You want to bet that > your Proxy got *all* of the methods right? This > interface didn't get that way all at once; it grew. > The number was 78 in Smalltalk-80. At a minimum, then, > Smalltalk systems have accreted one extra Object method > every two months. > > So you set up your proxy to *flawlesly* mirror Object, > and then, WHOOPS, upgrade Smalltalk and now there is a > method that Object has and your Proxy either lacks (if > it descends from ProtoObject but not Object) or inherits > an inappropriate version of (if it descends from Object). > > What this means is that nobody ever *does* flawlessly > mock everything in the public interface of an object > they are Proxying. They proxy a *limited* protocol. > Because that is all they *can* do. > > Look, I know that people who have been trained to work > with the stuff can use C4 as cooking fuel. But I haven't > had that training, so I won't touch the stuff. In the > same way, I dare say there are things *you* can safely > do in Smalltalk that fumblefingers here would be burnt > badly by. There are many things that *can* be done that > I *won't* do. In a chemistry lab, I would not work with > ClF3 let alone O2F2. In Smalltalk, I don't monkey with > #isNil. > > On Fri, 18 Mar 2022 at 03:52, James Foster <smalltalk(a)jgfoster.net> wrote: > >> Richard, >> >> I very much admire Dijkstraâs admonition regarding âThe Humble >> Programmerâ and was pointing a student to that article just this week. >> >> In any case, I think youâve demonstrated that you now comprehend the >> argument against inliningâyou just donât agree. Thatâs fair and I think the >> discussion has been clarified. Would it be fair to say that you have an >> âideological objectionâ to allowing a Proxy or Stub to transparently stand >> in for another object (say, in a two-object-space environment such as Pharo >> and GemStone)? That is, a domain object canât be replaced by a Proxy or >> Stub without a wholesale rewrite of the rest of the application? I respect >> that as a reasonable position (demanding perfect clarity), but I see a cost >> to that position as well. >> >> Of course, if you really want to avoid allowing the receiver to chose its >> response to a message, you can use other messages. So if you want to find >> out if an object is identical to nil you should use `nil == myObject` to >> ensure that there was not an override of #âisNilâ or #â==â by the objectâs >> class. >> >> James >> >> On Mar 17, 2022, at 2:27 AM, Richard O'Keefe <raoknz(a)gmail.com> wrote: >> >> My chief concern is that I am a bear of very little brain, >> and if you change the meaning of #isNil to anything at all >> other than "is the receiver identical to nil" you *WILL* >> (not may) confuse me. This extends to things that happen >> not to be inlined: if even a god-like Smalltalker like >> Andres Valloud overloads #, to something other than "combine >> the collection that is the receiver with the collection that >> is the argument to yield a new collection" than I *WILL* >> most certainly be confused and find the code unmaintainable. >> Smalltalk being Smalltalk, if you admit an inconsistent >> overload anywhere, I can no longer understand sends of that >> selector anywhere. One of the things to like about Traits >> is that you can say "this class doesn't just *happen* to >> have selectors x and y, it has them *because* it has this >> whole consistent bundle of selectors." >> >> There are more annotations documented for my Smalltalk >> compiler than are actually implemented. One that *is* >> implemented is <doNotOverride>, and it has caught more >> mistakes than I care to admit to. It's particularly >> important for a bundle of methods with varying arguments >> that are meant to be routed through a single method, >> which *is* meant to be overridden. It makes sure that >> I override the *right* method. (Take #= and #~= as an >> obvious example.) >> >> Once you start down the path of lying about things like #isNil >> you find that EITHER you have to go very far down that path >> and override #== and #instVarAt: and a whole lot of other >> things OR you are working with a semantically incoherent system. >> >> "How should a proxy (https://en.wikipedia.org/wiki/Proxy_pattern) to nil >> respond to the #âisNilâ message?" >> >> It SHOULD NOT LIE. A proxy *isn't* nil, and it doesn't *behave* like nil, >> even if it is a proxy for nil. A proxy, qua proxy, can do things that nil >> cannot. Use another selector, #isEffectivelyNil, or whatever reveals your >> intentions, and give it what semantics you find useful. >> >> "How should the Null Object Pattern ( >> https://en.wikipedia.org/wiki/Null_object_pattern) respond to #âisNilâ?" >> >> It should answer false. Period. No ifs, buts, quibbles, or maybes. >> The whole *point* of the Null Object Pattern is to return something >> that *isn't* nil, that has quite a different protocol. If you call >> something that is supposed to return either a Foo or a NullFoo, and >> it gives you nil instead, there is a BUG in what you just called so >> the sooner you find out the better. What you want is >> >> Foo >> isNullFoo ^false >> NullFoo >> isNullFoo ^true >> and no other class defines #isNullFoo. >> >> That way, when you ask "tripeWorks grobblingMill lastPallet isNullPallet" >> (a) you make it clear to someone reading your code what you are expecting >> (b) if you DON'T get what you are expecting, Smalltalk will tell you. >> >> I must admit that on the few occasions when I've used Null Object >> I've used an all-purpose #isMissing instead of a task-appropriate >> #isNullFoo, but then I figured out what I was doing wrong. You >> look at the code, you say "there's *something* off here, but I don't >> know what." But when you ask "what, exactly, does this method MEAN?" >> you realise "oh, THAT'S what I was doing wrong." #isMissing told me >> it was a NullPerson or a NullAddress or a NullPartsList or ... but >> in this case I needed to know whether it was a NullSummary. >> >> And of course you run into E.F.Codd's lesson: "one NULL is never >> enough, information can be missing for more than one reason". >> Take the familiar example of a phone number: >> - I know that Fred's phone number is X >> - I know that Fred has a phone but I don't know what the number is >> - I don't know whether Fred has a phone or not >> - I know that Fred has no phone >> There's room for three *different* null objects there. >> Should we have UnknownNumberOfActualPhone to answer false to #isnil >> and NonNumberOfNonexistentPhone to answer true? Or what? >> >> By the way, you may have misunderstood my benchmark. >> It wasn't that #isNil or even _ ifNotNil: speeded up by >> 10%, it was the *whole* matrix-munching benchmark that >> speeded up. Certainly not a big deal, but it's not >> something I'd be happy to give up in order to get less >> maintainable code. >> >> >> >> >> >> >> >> >> On Thu, 17 Mar 2022 at 18:21, James Foster <smalltalk(a)jgfoster.net> >> wrote: >> >>> Richard, >>> >>> My _concern_ with inlining is that since it is designed to short-circuit >>> dynamic method lookup, it is impossible to call a _different_ >>> implementation. That is, you lose the opportunity to have the _receiver_ >>> decide how to respond to the message. You may think of it as a message, but >>> the caller is deciding how the receiver will respondâwhich largely defeats >>> the purpose and role of it being a message. Yes, at the machine code level >>> you are performing a branch instruction, but when comparing OOP to >>> Procedural Programming we typically make a distinction between âmessagesâ >>> and "procedure calls." The distinction is that the receiver gets to decide >>> how to respond to a message. In C++ this is the distinction between a >>> âvirtual" and "non-virtual" function. By inlining, you are converting the >>> function from a virtual function to a non-virtual function, and this can >>> make a difference (which is why virtual functions exist). >>> >>> How should a proxy (https://en.wikipedia.org/wiki/Proxy_pattern) to nil >>> respond to the #âisNilâ message? How should the Null Object Pattern ( >>> https://en.wikipedia.org/wiki/Null_object_pattern) respond to #âisNilâ? >>> >>> And, yes, Iâm sure you can come up with benchmarks that show a >>> measurable difference, but what is the impact in realistic code? When >>> someone asked about inlining #âyourselfâ in GemStone I believe I measured >>> the performance as taking 2 nanoseconds per call (on a 2012 machine). A 10% >>> speedup would make it 1.8 nanoseconds. Is that worth it? Maybe, maybe not. >>> >>> Note that I described my position as a âconcern,â not an ideological >>> objection. Mostly Iâm giving a rationale for something that doesnât seem to >>> be explained very well for you. I accept that there may be a time for >>> inlining, but I can âcomprehend" another side to the issue. >>> >>> James >>> >>> On Mar 16, 2022, at 9:42 PM, Richard O'Keefe <raoknz(a)gmail.com> wrote: >>> >>> We're still not on the same page. >>> You seem to have some ideological objection to inlining that >>> I am completely failing to comprehend. >>> Just because a procedure call (message send) is inlined doesn't >>> in the least mean it *isn't* a procedure call (message send), >>> just as compiling a procedure call (message send) as a jump >>> (last-call optimisation) doesn't mean it *isn't* a procedure >>> call (message send). >>> By the way, forget about "40 years ago". >>> I just did an experiment in Pharo 9, and found that >>> using "_ ifNotNil: " instead of "_ izNil ifFalse: " >>> -- where izNil is a non-inlined self == nil -- >>> gave a 10% speedup, in a test code where real work was going >>> on as well. >>> As for turning off all inlining, what do you think that would >>> do to #ifFalse:ifTrue: and its relatives? >>> >>> >>> On Thu, 17 Mar 2022 at 08:34, <sean(a)clipperadams.com> wrote: >>> >>>> >>>> To start with, why do you CARE whether a particular method is inlined >>>> or not? >>>> >>>> I care because it makes âeverything is a messageâ a lie! And I suspect >>>> (no proof and could be wrong) itâs an optimization that only made sense >>>> with the hardware constraints of 40+ years ago. Arguing against premature >>>> optimization is hardly something I just made up ;-) >>>> >>>> This makes absolutely no sense to me. What makes you think that the >>>> combination "_ isNil ifFalse: [_]" will NOT be inlined? >>>> >>>> I may have been unclear. My intent was to communicate: âIâd like to >>>> stop ALL* inlining of messages by default if possibleâ >>>> >>>> *or as many as practical >>>> >>>> The thing that rings loud alarm bells for me is there being "long >>>> chains" in the first place. >>>> >>>> I agree that it is in general a smell, but long chains was tangential >>>> to the intention above >>>> >>>> Can you give an example? >>>> >>>> I donât know if I can think of one thatâs not contrivedâ¦ Wrapping >>>> something external? Squeakâs AppleScript support used to mirror the >>>> underlying AS, which is pretty much exactly that. >>>> >>>> In my own programming, I've generally found that nils turning up in the >>>> middle of a chain indicates a serious design error somewhere. >>>> >>>> Agreed. See smell comment above. >>>> >>> >>> >> >

March 20, 2022

Re: Null Object Pattern

by James Foster

I donât understand. Wouldnât an override of #'doesNotUnderstand:â solve this problem? The proxies Iâve seen subclass from nil or ProtoObject and forward almost everything to the target. Itâs really very easy. > On Mar 19, 2022, at 3:14 AM, Richard O'Keefe <raoknz(a)gmail.com> wrote: > > An object should be a Proxy or Stub only with reference to a specific protocol, which should be kept narrow. > > Being a Proxy is a form of coupling. Proxying a wide > interface creates maintenance problems: > Squeak 5.3 : Object selectors size => 485 > Pharo 9.0 : Object selectors size => 435 > astc : Object selectors size => 325 > VW 8.3PUL : Object selectors size => 304 > > The interface of Object is HUGE. You want to bet that > your Proxy got *all* of the methods right? This > interface didn't get that way all at once; it grew. > The number was 78 in Smalltalk-80. At a minimum, then, > Smalltalk systems have accreted one extra Object method > every two months. > > So you set up your proxy to *flawlesly* mirror Object, > and then, WHOOPS, upgrade Smalltalk and now there is a > method that Object has and your Proxy either lacks (if > it descends from ProtoObject but not Object) or inherits > an inappropriate version of (if it descends from Object). > > What this means is that nobody ever *does* flawlessly > mock everything in the public interface of an object > they are Proxying. They proxy a *limited* protocol. > Because that is all they *can* do. > > Look, I know that people who have been trained to work > with the stuff can use C4 as cooking fuel. But I haven't > had that training, so I won't touch the stuff. In the > same way, I dare say there are things *you* can safely > do in Smalltalk that fumblefingers here would be burnt > badly by. There are many things that *can* be done that > I *won't* do. In a chemistry lab, I would not work with > ClF3 let alone O2F2. In Smalltalk, I don't monkey with > #isNil. > > On Fri, 18 Mar 2022 at 03:52, James Foster <smalltalk(a)jgfoster.net <mailto:smalltalk@jgfoster.net>> wrote: > Richard, > > I very much admire Dijkstraâs admonition regarding âThe Humble Programmerâ and was pointing a student to that article just this week. > > In any case, I think youâve demonstrated that you now comprehend the argument against inliningâyou just donât agree. Thatâs fair and I think the discussion has been clarified. Would it be fair to say that you have an âideological objectionâ to allowing a Proxy or Stub to transparently stand in for another object (say, in a two-object-space environment such as Pharo and GemStone)? That is, a domain object canât be replaced by a Proxy or Stub without a wholesale rewrite of the rest of the application? I respect that as a reasonable position (demanding perfect clarity), but I see a cost to that position as well. > > Of course, if you really want to avoid allowing the receiver to chose its response to a message, you can use other messages. So if you want to find out if an object is identical to nil you should use `nil == myObject` to ensure that there was not an override of #âisNilâ or #â==â by the objectâs class. > > James > >> On Mar 17, 2022, at 2:27 AM, Richard O'Keefe <raoknz(a)gmail.com <mailto:raoknz@gmail.com>> wrote: >> >> My chief concern is that I am a bear of very little brain, >> and if you change the meaning of #isNil to anything at all >> other than "is the receiver identical to nil" you *WILL* >> (not may) confuse me. This extends to things that happen >> not to be inlined: if even a god-like Smalltalker like >> Andres Valloud overloads #, to something other than "combine >> the collection that is the receiver with the collection that >> is the argument to yield a new collection" than I *WILL* >> most certainly be confused and find the code unmaintainable. >> Smalltalk being Smalltalk, if you admit an inconsistent >> overload anywhere, I can no longer understand sends of that >> selector anywhere. One of the things to like about Traits >> is that you can say "this class doesn't just *happen* to >> have selectors x and y, it has them *because* it has this >> whole consistent bundle of selectors." >> >> There are more annotations documented for my Smalltalk >> compiler than are actually implemented. One that *is* >> implemented is <doNotOverride>, and it has caught more >> mistakes than I care to admit to. It's particularly >> important for a bundle of methods with varying arguments >> that are meant to be routed through a single method, >> which *is* meant to be overridden. It makes sure that >> I override the *right* method. (Take #= and #~= as an >> obvious example.) >> >> Once you start down the path of lying about things like #isNil >> you find that EITHER you have to go very far down that path >> and override #== and #instVarAt: and a whole lot of other >> things OR you are working with a semantically incoherent system. >> >> "How should a proxy (https://en.wikipedia.org/wiki/Proxy_pattern <https://en.wikipedia.org/wiki/Proxy_pattern>) to nil respond to the #âisNilâ message?" >> >> It SHOULD NOT LIE. A proxy *isn't* nil, and it doesn't *behave* like nil, >> even if it is a proxy for nil. A proxy, qua proxy, can do things that nil >> cannot. Use another selector, #isEffectivelyNil, or whatever reveals your >> intentions, and give it what semantics you find useful. >> >> "How should the Null Object Pattern (https://en.wikipedia.org/wiki/Null_object_pattern <https://en.wikipedia.org/wiki/Null_object_pattern>) respond to #âisNilâ?" >> >> It should answer false. Period. No ifs, buts, quibbles, or maybes. >> The whole *point* of the Null Object Pattern is to return something >> that *isn't* nil, that has quite a different protocol. If you call >> something that is supposed to return either a Foo or a NullFoo, and >> it gives you nil instead, there is a BUG in what you just called so >> the sooner you find out the better. What you want is >> >> Foo >> isNullFoo ^false >> NullFoo >> isNullFoo ^true >> and no other class defines #isNullFoo. >> >> That way, when you ask "tripeWorks grobblingMill lastPallet isNullPallet" >> (a) you make it clear to someone reading your code what you are expecting >> (b) if you DON'T get what you are expecting, Smalltalk will tell you. >> >> I must admit that on the few occasions when I've used Null Object >> I've used an all-purpose #isMissing instead of a task-appropriate >> #isNullFoo, but then I figured out what I was doing wrong. You >> look at the code, you say "there's *something* off here, but I don't >> know what." But when you ask "what, exactly, does this method MEAN?" >> you realise "oh, THAT'S what I was doing wrong." #isMissing told me >> it was a NullPerson or a NullAddress or a NullPartsList or ... but >> in this case I needed to know whether it was a NullSummary. >> >> And of course you run into E.F.Codd's lesson: "one NULL is never >> enough, information can be missing for more than one reason". >> Take the familiar example of a phone number: >> - I know that Fred's phone number is X >> - I know that Fred has a phone but I don't know what the number is >> - I don't know whether Fred has a phone or not >> - I know that Fred has no phone >> There's room for three *different* null objects there. >> Should we have UnknownNumberOfActualPhone to answer false to #isnil >> and NonNumberOfNonexistentPhone to answer true? Or what? >> >> By the way, you may have misunderstood my benchmark. >> It wasn't that #isNil or even _ ifNotNil: speeded up by >> 10%, it was the *whole* matrix-munching benchmark that >> speeded up. Certainly not a big deal, but it's not >> something I'd be happy to give up in order to get less >> maintainable code. >> >> >> >> >> >> >> >> >> On Thu, 17 Mar 2022 at 18:21, James Foster <smalltalk(a)jgfoster.net <mailto:smalltalk@jgfoster.net>> wrote: >> Richard, >> >> My _concern_ with inlining is that since it is designed to short-circuit dynamic method lookup, it is impossible to call a _different_ implementation. That is, you lose the opportunity to have the _receiver_ decide how to respond to the message. You may think of it as a message, but the caller is deciding how the receiver will respondâwhich largely defeats the purpose and role of it being a message. Yes, at the machine code level you are performing a branch instruction, but when comparing OOP to Procedural Programming we typically make a distinction between âmessagesâ and "procedure calls." The distinction is that the receiver gets to decide how to respond to a message. In C++ this is the distinction between a âvirtual" and "non-virtual" function. By inlining, you are converting the function from a virtual function to a non-virtual function, and this can make a difference (which is why virtual functions exist). >> >> How should a proxy (https://en.wikipedia.org/wiki/Proxy_pattern <https://en.wikipedia.org/wiki/Proxy_pattern>) to nil respond to the #âisNilâ message? How should the Null Object Pattern (https://en.wikipedia.org/wiki/Null_object_pattern <https://en.wikipedia.org/wiki/Null_object_pattern>) respond to #âisNilâ? >> >> And, yes, Iâm sure you can come up with benchmarks that show a measurable difference, but what is the impact in realistic code? When someone asked about inlining #âyourselfâ in GemStone I believe I measured the performance as taking 2 nanoseconds per call (on a 2012 machine). A 10% speedup would make it 1.8 nanoseconds. Is that worth it? Maybe, maybe not. >> >> Note that I described my position as a âconcern,â not an ideological objection. Mostly Iâm giving a rationale for something that doesnât seem to be explained very well for you. I accept that there may be a time for inlining, but I can âcomprehend" another side to the issue. >> >> James >> >>> On Mar 16, 2022, at 9:42 PM, Richard O'Keefe <raoknz(a)gmail.com <mailto:raoknz@gmail.com>> wrote: >>> >>> We're still not on the same page. >>> You seem to have some ideological objection to inlining that >>> I am completely failing to comprehend. >>> Just because a procedure call (message send) is inlined doesn't >>> in the least mean it *isn't* a procedure call (message send), >>> just as compiling a procedure call (message send) as a jump >>> (last-call optimisation) doesn't mean it *isn't* a procedure >>> call (message send). >>> By the way, forget about "40 years ago". >>> I just did an experiment in Pharo 9, and found that >>> using "_ ifNotNil: " instead of "_ izNil ifFalse: " >>> -- where izNil is a non-inlined self == nil -- >>> gave a 10% speedup, in a test code where real work was going >>> on as well. >>> As for turning off all inlining, what do you think that would >>> do to #ifFalse:ifTrue: and its relatives? >>> >>> >>> On Thu, 17 Mar 2022 at 08:34, <sean(a)clipperadams.com <mailto:sean@clipperadams.com>> wrote: >>> >>> >>> To start with, why do you CARE whether a particular method is inlined or not? >>> >>> I care because it makes âeverything is a messageâ a lie! And I suspect (no proof and could be wrong) itâs an optimization that only made sense with the hardware constraints of 40+ years ago. Arguing against premature optimization is hardly something I just made up ;-) >>> >>> This makes absolutely no sense to me. What makes you think that the combination "_ isNil ifFalse: [_]" will NOT be inlined? >>> >>> I may have been unclear. My intent was to communicate: âIâd like to stop ALL* inlining of messages by default if possibleâ >>> >>> *or as many as practical >>> >>> The thing that rings loud alarm bells for me is there being "long chains" in the first place. >>> >>> I agree that it is in general a smell, but long chains was tangential to the intention above >>> >>> Can you give an example? >>> >>> I donât know if I can think of one thatâs not contrivedâ¦ Wrapping something external? Squeakâs AppleScript support used to mirror the underlying AS, which is pretty much exactly that. >>> >>> In my own programming, I've generally found that nils turning up in the middle of a chain indicates a serious design error somewhere. >>> >>> Agreed. See smell comment above. >>> >> >

March 20, 2022

Re: Null Object Pattern

by Richard O'Keefe

An object should be a Proxy or Stub only with reference to a specific protocol, which should be kept narrow. Being a Proxy is a form of coupling. Proxying a wide interface creates maintenance problems: Squeak 5.3 : Object selectors size => 485 Pharo 9.0 : Object selectors size => 435 astc : Object selectors size => 325 VW 8.3PUL : Object selectors size => 304 The interface of Object is HUGE. You want to bet that your Proxy got *all* of the methods right? This interface didn't get that way all at once; it grew. The number was 78 in Smalltalk-80. At a minimum, then, Smalltalk systems have accreted one extra Object method every two months. So you set up your proxy to *flawlesly* mirror Object, and then, WHOOPS, upgrade Smalltalk and now there is a method that Object has and your Proxy either lacks (if it descends from ProtoObject but not Object) or inherits an inappropriate version of (if it descends from Object). What this means is that nobody ever *does* flawlessly mock everything in the public interface of an object they are Proxying. They proxy a *limited* protocol. Because that is all they *can* do. Look, I know that people who have been trained to work with the stuff can use C4 as cooking fuel. But I haven't had that training, so I won't touch the stuff. In the same way, I dare say there are things *you* can safely do in Smalltalk that fumblefingers here would be burnt badly by. There are many things that *can* be done that I *won't* do. In a chemistry lab, I would not work with ClF3 let alone O2F2. In Smalltalk, I don't monkey with #isNil. On Fri, 18 Mar 2022 at 03:52, James Foster <smalltalk(a)jgfoster.net> wrote: > Richard, > > I very much admire Dijkstraâs admonition regarding âThe Humble Programmerâ > and was pointing a student to that article just this week. > > In any case, I think youâve demonstrated that you now comprehend the > argument against inliningâyou just donât agree. Thatâs fair and I think the > discussion has been clarified. Would it be fair to say that you have an > âideological objectionâ to allowing a Proxy or Stub to transparently stand > in for another object (say, in a two-object-space environment such as Pharo > and GemStone)? That is, a domain object canât be replaced by a Proxy or > Stub without a wholesale rewrite of the rest of the application? I respect > that as a reasonable position (demanding perfect clarity), but I see a cost > to that position as well. > > Of course, if you really want to avoid allowing the receiver to chose its > response to a message, you can use other messages. So if you want to find > out if an object is identical to nil you should use `nil == myObject` to > ensure that there was not an override of #âisNilâ or #â==â by the objectâs > class. > > James > > On Mar 17, 2022, at 2:27 AM, Richard O'Keefe <raoknz(a)gmail.com> wrote: > > My chief concern is that I am a bear of very little brain, > and if you change the meaning of #isNil to anything at all > other than "is the receiver identical to nil" you *WILL* > (not may) confuse me. This extends to things that happen > not to be inlined: if even a god-like Smalltalker like > Andres Valloud overloads #, to something other than "combine > the collection that is the receiver with the collection that > is the argument to yield a new collection" than I *WILL* > most certainly be confused and find the code unmaintainable. > Smalltalk being Smalltalk, if you admit an inconsistent > overload anywhere, I can no longer understand sends of that > selector anywhere. One of the things to like about Traits > is that you can say "this class doesn't just *happen* to > have selectors x and y, it has them *because* it has this > whole consistent bundle of selectors." > > There are more annotations documented for my Smalltalk > compiler than are actually implemented. One that *is* > implemented is <doNotOverride>, and it has caught more > mistakes than I care to admit to. It's particularly > important for a bundle of methods with varying arguments > that are meant to be routed through a single method, > which *is* meant to be overridden. It makes sure that > I override the *right* method. (Take #= and #~= as an > obvious example.) > > Once you start down the path of lying about things like #isNil > you find that EITHER you have to go very far down that path > and override #== and #instVarAt: and a whole lot of other > things OR you are working with a semantically incoherent system. > > "How should a proxy (https://en.wikipedia.org/wiki/Proxy_pattern) to nil > respond to the #âisNilâ message?" > > It SHOULD NOT LIE. A proxy *isn't* nil, and it doesn't *behave* like nil, > even if it is a proxy for nil. A proxy, qua proxy, can do things that nil > cannot. Use another selector, #isEffectivelyNil, or whatever reveals your > intentions, and give it what semantics you find useful. > > "How should the Null Object Pattern ( > https://en.wikipedia.org/wiki/Null_object_pattern) respond to #âisNilâ?" > > It should answer false. Period. No ifs, buts, quibbles, or maybes. > The whole *point* of the Null Object Pattern is to return something > that *isn't* nil, that has quite a different protocol. If you call > something that is supposed to return either a Foo or a NullFoo, and > it gives you nil instead, there is a BUG in what you just called so > the sooner you find out the better. What you want is > > Foo >> isNullFoo ^false > NullFoo >> isNullFoo ^true > and no other class defines #isNullFoo. > > That way, when you ask "tripeWorks grobblingMill lastPallet isNullPallet" > (a) you make it clear to someone reading your code what you are expecting > (b) if you DON'T get what you are expecting, Smalltalk will tell you. > > I must admit that on the few occasions when I've used Null Object > I've used an all-purpose #isMissing instead of a task-appropriate > #isNullFoo, but then I figured out what I was doing wrong. You > look at the code, you say "there's *something* off here, but I don't > know what." But when you ask "what, exactly, does this method MEAN?" > you realise "oh, THAT'S what I was doing wrong." #isMissing told me > it was a NullPerson or a NullAddress or a NullPartsList or ... but > in this case I needed to know whether it was a NullSummary. > > And of course you run into E.F.Codd's lesson: "one NULL is never > enough, information can be missing for more than one reason". > Take the familiar example of a phone number: > - I know that Fred's phone number is X > - I know that Fred has a phone but I don't know what the number is > - I don't know whether Fred has a phone or not > - I know that Fred has no phone > There's room for three *different* null objects there. > Should we have UnknownNumberOfActualPhone to answer false to #isnil > and NonNumberOfNonexistentPhone to answer true? Or what? > > By the way, you may have misunderstood my benchmark. > It wasn't that #isNil or even _ ifNotNil: speeded up by > 10%, it was the *whole* matrix-munching benchmark that > speeded up. Certainly not a big deal, but it's not > something I'd be happy to give up in order to get less > maintainable code. > > > > > > > > > On Thu, 17 Mar 2022 at 18:21, James Foster <smalltalk(a)jgfoster.net> wrote: > >> Richard, >> >> My _concern_ with inlining is that since it is designed to short-circuit >> dynamic method lookup, it is impossible to call a _different_ >> implementation. That is, you lose the opportunity to have the _receiver_ >> decide how to respond to the message. You may think of it as a message, but >> the caller is deciding how the receiver will respondâwhich largely defeats >> the purpose and role of it being a message. Yes, at the machine code level >> you are performing a branch instruction, but when comparing OOP to >> Procedural Programming we typically make a distinction between âmessagesâ >> and "procedure calls." The distinction is that the receiver gets to decide >> how to respond to a message. In C++ this is the distinction between a >> âvirtual" and "non-virtual" function. By inlining, you are converting the >> function from a virtual function to a non-virtual function, and this can >> make a difference (which is why virtual functions exist). >> >> How should a proxy (https://en.wikipedia.org/wiki/Proxy_pattern) to nil >> respond to the #âisNilâ message? How should the Null Object Pattern ( >> https://en.wikipedia.org/wiki/Null_object_pattern) respond to #âisNilâ? >> >> And, yes, Iâm sure you can come up with benchmarks that show a measurable >> difference, but what is the impact in realistic code? When someone asked >> about inlining #âyourselfâ in GemStone I believe I measured the performance >> as taking 2 nanoseconds per call (on a 2012 machine). A 10% speedup would >> make it 1.8 nanoseconds. Is that worth it? Maybe, maybe not. >> >> Note that I described my position as a âconcern,â not an ideological >> objection. Mostly Iâm giving a rationale for something that doesnât seem to >> be explained very well for you. I accept that there may be a time for >> inlining, but I can âcomprehend" another side to the issue. >> >> James >> >> On Mar 16, 2022, at 9:42 PM, Richard O'Keefe <raoknz(a)gmail.com> wrote: >> >> We're still not on the same page. >> You seem to have some ideological objection to inlining that >> I am completely failing to comprehend. >> Just because a procedure call (message send) is inlined doesn't >> in the least mean it *isn't* a procedure call (message send), >> just as compiling a procedure call (message send) as a jump >> (last-call optimisation) doesn't mean it *isn't* a procedure >> call (message send). >> By the way, forget about "40 years ago". >> I just did an experiment in Pharo 9, and found that >> using "_ ifNotNil: " instead of "_ izNil ifFalse: " >> -- where izNil is a non-inlined self == nil -- >> gave a 10% speedup, in a test code where real work was going >> on as well. >> As for turning off all inlining, what do you think that would >> do to #ifFalse:ifTrue: and its relatives? >> >> >> On Thu, 17 Mar 2022 at 08:34, <sean(a)clipperadams.com> wrote: >> >>> >>> To start with, why do you CARE whether a particular method is inlined or >>> not? >>> >>> I care because it makes âeverything is a messageâ a lie! And I suspect >>> (no proof and could be wrong) itâs an optimization that only made sense >>> with the hardware constraints of 40+ years ago. Arguing against premature >>> optimization is hardly something I just made up ;-) >>> >>> This makes absolutely no sense to me. What makes you think that the >>> combination "_ isNil ifFalse: [_]" will NOT be inlined? >>> >>> I may have been unclear. My intent was to communicate: âIâd like to stop >>> ALL* inlining of messages by default if possibleâ >>> >>> *or as many as practical >>> >>> The thing that rings loud alarm bells for me is there being "long >>> chains" in the first place. >>> >>> I agree that it is in general a smell, but long chains was tangential to >>> the intention above >>> >>> Can you give an example? >>> >>> I donât know if I can think of one thatâs not contrivedâ¦ Wrapping >>> something external? Squeakâs AppleScript support used to mirror the >>> underlying AS, which is pretty much exactly that. >>> >>> In my own programming, I've generally found that nils turning up in the >>> middle of a chain indicates a serious design error somewhere. >>> >>> Agreed. See smell comment above. >>> >> >> >

March 19, 2022

Re: Null Object Pattern

by Todd Blanchard

> On Mar 18, 2022, at 11:39 AM, Esteban Maringolo <emaringolo(a)gmail.com> wrote: > > You say that Smalltalk is not so hot for system developments because > it's extremely malleable? What are you measuring it against? Lots of things but to keep things simple lets go with Objective C since it is quite similar in concept and style but the library classes are closed to modification without extraordinary effort (you can replace a method but you're gonna have to work to do it because you don't have the source code for the core classes). > > It is still easy to break almost anything, without having to resort to > compiler pragmas. :-) Yeah, that's kind of my point. I have junked a lot of images in my wake. >> If anything, I would like to see more immutable structure in the core classes. Add methods? Always. Casually override anything? There be dragons there. > > Something like "final" classes and "const" globals or not being able > to extend classes such as [Proto]Object? IDK exactly. Yeah, maybe a pragma that was part of the core library that would prevent an override of a key method that say, the browser, depends on. Smalltalk is great for building things, but unlike when I build, say, a car, I don't have to drag around the entire factory I used to build the car behind it everywhere. Toying with the idea of using one image to host remote developer tools that we do not change and using it to operate on a second image that has minimal dev tools but will be the production version of my app. That would provide the separation that would keep me from destroying toolkit by accident while trying to tweak the app. Just musing here. I've become kind of dissatisfied with Pharo development of late. Hard to build anything that lasts very long. > > > >> >> On Mar 18, 2022, at 11:06 AM, sean(a)clipperadams.com wrote: >> >> I feel like youâve latched onto something that is genuinely a non problemâ¦ >> >> I wouldnât call complexity and lack of consistency a ânon problemâ, but it sounds like for you the practical implications outweigh my seemingly-somewhat-ideological/niche concerns. Is that a fair summary? In any case, I appreciate your perspective. >> >>

March 18, 2022

Re: Null Object Pattern

by Esteban Maringolo

On Fri, Mar 18, 2022 at 3:24 PM Todd Blanchard via Pharo-users <pharo-users(a)lists.pharo.org> wrote: > > What, exactly, is inconsistent about a key message isNil being allowed to be overridden? Overrides are not the issue here. > There is a VERY simple solution to your problem that does not involve disrupting the platform. No, it's not a simple solution. > But you'd rather change the platform. I'd bet that the change to inline those message sends came after the implementation of the message sending. > Part of the reason Smalltalk has not been the greatest platform to build software on is its extreme malleability. It is a double edged sword for sure. It is great for research. Not so hot for actual systems development. You say that Smalltalk is not so hot for system developments because it's extremely malleable? What are you measuring it against? > "The key in making great and growable systems is much more to design how its modules communicate rather than what their internal properties and behaviors should be. <trim>" -Alan Kay That's exactly the point of this conversion, a user might want the modules to communicate by means of sending messages between them, so writes the code with that expectation and then an external thing (the compiler) decides to do something else that involves not actually sending the message, because it focuses on the "internal properties and behaviors". > The inlined methods implement key operations that I believe *should* be immutable. Because the system is implemented in terms of itself, it is not very hard to completely destroy an image and render it unusable by overriding the wrong message in the wrong class (try overriding #environment at the class level and let me know how long before your image completely packs up under a torrent of walkbacks). It is still easy to break almost anything, without having to resort to compiler pragmas. :-) > If anything, I would like to see more immutable structure in the core classes. Add methods? Always. Casually override anything? There be dragons there. Something like "final" classes and "const" globals or not being able to extend classes such as [Proto]Object? In any case, I think the options for this inlining thing were laid on the table, and there is a partial solution for these looking for "semantic optimization" (as in true message sends) rather than performance optimization (as in inlining). Regards! Esteban A. Maringolo > > On Mar 18, 2022, at 11:06 AM, sean(a)clipperadams.com wrote: > > I feel like youâve latched onto something that is genuinely a non problemâ¦ > > I wouldnât call complexity and lack of consistency a ânon problemâ, but it sounds like for you the practical implications outweigh my seemingly-somewhat-ideological/niche concerns. Is that a fair summary? In any case, I appreciate your perspective. > >

March 18, 2022