anObject select: #aMethodName -- is this good Squeak?

> From: Michael Davies
> Sent: Wednesday, February 07, 2007 1:07 PM
>
> I was browsing some of the Magritte source code, when I saw a message
> that confused me:
> selectors := anObject class allSelectors
> select: #isDescriptionSelector.
>
> I couldn't understand how you could pass a Symbol to #select: instead
> of a block -- certainly the definition of Collection>>select: implies
> it should only take a block. But trying it for myself, I see it works
> -- eg
> { 1. 2. 3. 4. } select: #even.
>
> can be used in place of:
>
> { 1. 2. 3. 4. } select: [ :each | each even ]
>
> Given how much simpler this looks, I was surprised I'd not seen this
> usage before, and searching for senders of #select: shows that the
> wordier version seems to be generally preferred.
>
> So my question is: is this a usage I should adopt or avoid?
>
> Cheers,
> Michael
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> Hi Michael,
>
> It's a trick.  It only works because #value: is implemented on symbol as:
>
> Symbol>>value: anObject
> ^anObject perform: self.
>
> So the following works too.
>
> #asUppercase value: 'I am a trick'
>
> My suggestion is that you shouldn't follow such tricks.  Although I do it
> too sometimes with things like.
>
> aDictionary at: #foo ifAbsent: nil.
>
> Since nil responds self to #value it seems redundant to me to put the nil in
> a block so that it can return nil when the block is evaluated with #value.
> Even though in this case the execution is faster but in the case of sending
> a symbol to select it is slower.
>
> In both cases it is harder to read so in my opinion it is best to stick with
> arguments that are expected.

> On 07/02/07, Giovanni Corriga wrote:
>>
>> Not to mention the fact that if you use a Symbol instead of a block,
>> that use won't be listed in the Senders browser.
>>
>>         Giovanni
>
> That was one of the things that I originally thought would weigh
> against this idiom, but found to my surprise that "Senders of"
> identified these references correctly-- I'd previously found symbols
> being included in my results and wondered why, but it looks as though
> someone was aware of this gotcha.

> > That was one of the things that I originally thought would weigh
> > against this idiom, but found to my surprise that "Senders of"
> > identified these references correctly-- I'd previously found symbols
> > being included in my results and wondered why, but it looks as though
> > someone was aware of this gotcha.
>
> Yes, browsing senders also works. Squeak puts all the data needed by a
> compiled method into a special place called literal array. So all
> selectors you send (expect special ones like #ifTrue:, #ifFalse:,
> #and:, #or, #whileTrue, ...) are in there, all symbols you use, all
> classes you reference, all strings and numbers. If you browse for
> senders, the system just looks at this literal array and doesn't make
> the difference if this is just a symbol or an actual selector of a
> message send.

> Il giorno gio, 08/02/2007 alle 07.53 +0100, Lukas Renggli ha scritto:
>> > That was one of the things that I originally thought would weigh
>> > against this idiom, but found to my surprise that "Senders of"
>> > identified these references correctly-- I'd previously found symbols
>> > being included in my results and wondered why, but it looks as though
>> > someone was aware of this gotcha.
>>
>> Yes, browsing senders also works. Squeak puts all the data needed by a
>> compiled method into a special place called literal array. So all
>> selectors you send (expect special ones like #ifTrue:, #ifFalse:,
>> #and:, #or, #whileTrue, ...) are in there, all symbols you use, all
>> classes you reference, all strings and numbers. If you browse for
>> senders, the system just looks at this literal array and doesn't make
>> the difference if this is just a symbol or an actual selector of a
>> message send.
>
> Does it? I tried browsing for senders on a 3.9 image before sending my
> message, and it didn't work.

> > Does it? I tried browsing for senders on a 3.9 image before sending my
> > message, and it didn't work.
>
> What was that symbol (for reproduction)?
>
> FWIW in #thoroughWhichSelectorsReferTo:special:byte: it is sought for  
> #allButLast of the method's literals. This can be a problem if the method  
> wasn't (re-)created after the image was traitified.
>
> Also, SystemNavigation>>#allCallsOn: is influenced by (Preferences  
> thoroughSenders).

> Il giorno gio, 08/02/2007 alle 11.37 +0100, Klaus D. Witzel ha scritto:
>> On Thu, 08 Feb 2007 10:21:53 +0100, Giovanni Corriga wrote:
>
>> > Does it? I tried browsing for senders on a 3.9 image before sending my
>> > message, and it didn't work.
>>
>> What was that symbol (for reproduction)?
>>
>> FWIW in #thoroughWhichSelectorsReferTo:special:byte: it is sought for
>> #allButLast of the method's literals. This can be a problem if the  
>> method
>> wasn't (re-)created after the image was traitified.
>>
>> Also, SystemNavigation>>#allCallsOn: is influenced by (Preferences
>> thoroughSenders).
>
> Ok, looking for senders from the Method Finder and/or the Message Finder
> works. But clicking on the Senders button on the browser doesn't show
> the symbol with the other selectors.
>
> I tested this by creating a bogus class and adding a method with this:
>
> #(1 2 3) select: #even.
>
> thoroughSenders is set.