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> 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. >> >
