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@jgfoster.net> wrote:
I don���t understand. Wouldn���t an override of #'doesNotUnderstand:��� solve this problem? The proxies I���ve seen subclass from nil or ProtoObject and forward almost everything to the target. It���s really very easy.

On Mar 19, 2022, at 3:14 AM, Richard O'Keefe <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@jgfoster.net> wrote:
Richard,

I very much admire Dijkstra���s admonition regarding ���The Humble Programmer��� and was pointing a student to that article just this week.��

In any case, I think you���ve demonstrated that you now comprehend the argument against inlining���you just don���t agree. That���s fair and I think the discussion has been clarified. Would it be fair to say that you have an ���ideological objection��� 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 can���t 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 #���isNil��� or #���==��� by the object���s class.��

James

On Mar 17, 2022, at 2:27 AM, Richard O'Keefe <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) to nil respond to the #���isNil��� 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 #���isNil���?"

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@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 respond���which 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 ���messages��� 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 ���virtual" 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 #���isNil��� message? How should the Null Object Pattern (https://en.wikipedia.org/wiki/Null_object_pattern) respond to #���isNil���?��

And, yes, I���m 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 #���yourself��� 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 ���concern,��� not an ideological objection. Mostly I���m giving a rationale for something that doesn���t seem to be explained very well for you. I accept that there may be a time for inlining, but I can ���comprehend" another side to the issue.

James

On Mar 16, 2022, at 9:42 PM, Richard O'Keefe <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@clipperadams.com> wrote:


To start with, why do you CARE whether a particular method is inlined or not?

I care because it makes ���everything is a message��� a lie! And I suspect (no proof and could be wrong) it���s 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: ���I���d like to stop ALL* inlining of messages by default if possible���

*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 don���t know if I can think of one that���s not contrived��� Wrapping something external? Squeak���s 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.