March 2022 - Pharo-users - lists.pharo.org

Re: Null Object Pattern

by Marcus Denker

> On 17 Mar 2022, at 18:00, Esteban Maringolo <emaringolo(a)gmail.com> wrote: > > That is great! > > Is it possible to disable it for doits and other playground expressions? > No, there is no hook yetâ¦ it would be interesting to see how to do that. (e.g. per playground compiler parameters, parameters for doit independent of the compiler used for compiling methodsâ¦) What you can do is turning it off globally in the setting (all compiler option are listed there) But take care: we can not recompile the image without optimzations as this adds intererrupt possibilities to code that was not interruptable before, which breaks the code in for process switching itself, I think. > Regards! > > Esteban A. Maringolo > > On Thu, Mar 17, 2022 at 1:23 PM Marcus Denker <marcus.denker(a)inria.fr> wrote: >> On 17 Mar 2022, at 17:17, Richard Sargent <richard.sargent(a)gemtalksystems.com> wrote: >> A pragma might be the way to go. >> <noInline: #and:> for example. >> >> >> >> There is already the #compilerOptions: Pragma, e.g.: >> >> <compilerOptions: #(- optionInlineAndOr )> >> For example this method compiled the and: as a real send: >> tt >> <compilerOptions: #(- optionInlineAndOr)> >> true and: [ false ] >> >> >> On Thu, Mar 17, 2022 at 8:17 AM Esteban Maringolo <emaringolo(a)gmail.com> wrote: > >>> A great trade off would be to be able >>> to enable/disable for certain things instead of it being a global >>> setting.

March 18, 2022

Re: Null Object Pattern

by Esteban Maringolo

That is great! Is it possible to disable it for doits and other playground expressions? Regards! Esteban A. Maringolo On Thu, Mar 17, 2022 at 1:23 PM Marcus Denker <marcus.denker(a)inria.fr> wrote: > On 17 Mar 2022, at 17:17, Richard Sargent <richard.sargent(a)gemtalksystems.com> wrote: > A pragma might be the way to go. > <noInline: #and:> for example. > > > > There is already the #compilerOptions: Pragma, e.g.: > > <compilerOptions: #(- optionInlineAndOr )> > For example this method compiled the and: as a real send: > tt > <compilerOptions: #(- optionInlineAndOr)> > true and: [ false ] > > > On Thu, Mar 17, 2022 at 8:17 AM Esteban Maringolo <emaringolo(a)gmail.com> wrote: >> A great trade off would be to be able >> to enable/disable for certain things instead of it being a global >> setting.

March 17, 2022

Re: Null Object Pattern

by Marcus Denker

> On 17 Mar 2022, at 17:17, Richard Sargent <richard.sargent(a)gemtalksystems.com> wrote: > > A pragma might be the way to go. > > <noInline: #and:> for example. There is already the #compilerOptions: Pragma, e.g.: <compilerOptions: #(- optionInlineAndOr )> For example this method compiled the and: as a real send: tt <compilerOptions: #(- optionInlineAndOr)> true and: [ false ] > > On Thu, Mar 17, 2022 at 8:17 AM Esteban Maringolo <emaringolo(a)gmail.com <mailto:emaringolo@gmail.com>> wrote: > Just to add another argument in favor of not inlining some message > sends, is for instance in things like Glorp you need to use a special > selector for #and:/#or: message sends, breaking not only the naming > conventions but also the polymorphism. > > E.g. you have to use #AND: and #OR: to avoid inlining. > db read: YourClass where: [:inst | inst name = 'John' AND: [inst color > = 'blue' OR: [inst color = 'red']]]. > > This is not only annoying, it also causes that if you want to to use > something else as a backend (instead of Glorp), your block doesn't > work anymore, which would perfectly work for a regular collection of > elements using their underscore #and:/#or: equivalents. > > The important thing, IMO, is that the core of OO is message sending, > and enabling the receiver what to do with a message, which in the > worst case would mean "I don't understand this message". A procedure > call inverts the responsibility. A great trade off would be to be able > to enable/disable for certain things instead of it being a global > setting. > > Regards, > > Esteban A. Maringolo > > On Thu, Mar 17, 2022 at 11:53 AM 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 17, 2022

Re: Null Object Pattern

by Richard Sargent

A pragma might be the way to go. *<noInline: #and:>* for example. On Thu, Mar 17, 2022 at 8:17 AM Esteban Maringolo <emaringolo(a)gmail.com> wrote: > Just to add another argument in favor of not inlining some message > sends, is for instance in things like Glorp you need to use a special > selector for #and:/#or: message sends, breaking not only the naming > conventions but also the polymorphism. > > E.g. you have to use #AND: and #OR: to avoid inlining. > db read: YourClass where: [:inst | inst name = 'John' AND: [inst color > = 'blue' OR: [inst color = 'red']]]. > > This is not only annoying, it also causes that if you want to to use > something else as a backend (instead of Glorp), your block doesn't > work anymore, which would perfectly work for a regular collection of > elements using their underscore #and:/#or: equivalents. > > The important thing, IMO, is that the core of OO is message sending, > and enabling the receiver what to do with a message, which in the > worst case would mean "I don't understand this message". A procedure > call inverts the responsibility. A great trade off would be to be able > to enable/disable for certain things instead of it being a global > setting. > > Regards, > > Esteban A. Maringolo > > On Thu, Mar 17, 2022 at 11:53 AM 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 17, 2022

Re: Null Object Pattern

by Esteban Maringolo

Just to add another argument in favor of not inlining some message sends, is for instance in things like Glorp you need to use a special selector for #and:/#or: message sends, breaking not only the naming conventions but also the polymorphism. E.g. you have to use #AND: and #OR: to avoid inlining. db read: YourClass where: [:inst | inst name = 'John' AND: [inst color = 'blue' OR: [inst color = 'red']]]. This is not only annoying, it also causes that if you want to to use something else as a backend (instead of Glorp), your block doesn't work anymore, which would perfectly work for a regular collection of elements using their underscore #and:/#or: equivalents. The important thing, IMO, is that the core of OO is message sending, and enabling the receiver what to do with a message, which in the worst case would mean "I don't understand this message". A procedure call inverts the responsibility. A great trade off would be to be able to enable/disable for certain things instead of it being a global setting. Regards, Esteban A. Maringolo On Thu, Mar 17, 2022 at 11:53 AM 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 17, 2022

[ANN] Stargate v7.1.1 [v7.1.1] released!

by Buenos Aires Smalltalk

March 17, 2022

Re: Null Object Pattern

by James Foster

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 <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 17, 2022

ANN: Linux Open Build Service new versions

by Esteban Lorenzano

Hi, I have been preparing our OBS builds [1] for the Pharo 10 release. We now include: Fedora 35 Ubuntu 21.10 Debian 11 And we fixed the rolling releases: Arch OpenSUSE Thumbleweed Enjoy! Esteban [1] https://software.opensuse.org//download.html?project=devel%3Alanguages%3Aph…

March 17, 2022

Re: Null Object Pattern

by Richard O'Keefe

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 17, 2022

Re: Null Object Pattern

by Kasper Osterbye

Sean When the compiler inlines some methods, I would find it most surprising if it was turned of in half the code (or just in yours :-) ). When I am reading some code, I would rather have some consistency. So I would just implement a whenNil: method which is a true message, and put a comment in its implementation so the next developer who comes by know why you did not just use ifNil: Best, Kasper

March 17, 2022