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 <rao...@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 <smallt...@jgfoster.net > <mailto:smallt...@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 <rao...@gmail.com >> <mailto:rao...@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 >> #’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 >> <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 <smallt...@jgfoster.net >> <mailto:smallt...@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 >> <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 >> <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 <rao...@gmail.com >>> <mailto:rao...@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, <s...@clipperadams.com >>> <mailto:s...@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. >>> >> >
