[Cuis-dev] unnecessary punctuation

[Jaromir Matas]

On 12-Jun-24 11:32:59 PM, "Mark Volkmann via Cuis-dev" 
<cuis-dev at lists.cuis.st> wrote:

>On Wed, Jun 12, 2024 at 4:28 PM Vanessa Freudenberg 
><vanessa at codefrau.net> wrote:
>>On Wed, Jun 12, 2024 at 6:56 AM Mark Volkmann via Cuis-dev 
>><cuis-dev at lists.cuis.st> wrote:
>>>I saw this example in a YouTube video about Smalltalk this morning:
>>>
>>>(2 > 3) ifTrue: ['Yes'] ifFalse: ['No']
>>>
>>>It seems to me that none of the parentheses or square brackets are 
>>>needed here.
>>>The following works the same for me.
>>>
>>>2 > 3 ifTrue: 'Yes' ifFalse: 'No'
>>>
>>>Is it true that keyword messages that take no-arg blocks can always 
>>>take a literal value instead?
>>>It seems this works because the `Object` class defines the `value` 
>>>method to just return `self`.
>>
>>Yes it only works because of Object>>value.
>
>I assumed that was intentional to support using objects that are not 
>blocks in cases like this.
>
>>It's also twice as slow to leave out the block brackets because it 
>>prevents compiler optimizations and forces actual sends to be made. 
>>You can verify that by benchmarking, and understand it by looking at 
>>the bytecodes generated and running a message tally.
>
>I believe you, but I'm curious why it's faster to send the `value:` 
>message to a block than to some other kind of object. Are you saying 
>that the optimizations make it so the `value:` message is not actually 
>sent to a block in this case and code in the block gets inlined?
>
 >> It's also twice as slow to leave out the block bracket [...]

Interesting - I've never realized the difference :) So if I understand 
correctly the #ifTrue:ifFalse message gets inlined only when used with 
block arguments, and it gets really sent when used without blocks; which 
means not only there's one more send but also that **both** 'Yes' and 
'No' expressions get evaluated before sending #ifTrue:ifFalse (hence 
twice as slow?). Inlining allows the runtime to evaluate only the 
"right" alternative. Here's the bytecode:

2 > 3 ifTrue: 'Yes' ifFalse: 'No'

49 pushConstant: 2
51 pushConstant: 3
53 send: >
54 pushConstant: 'Yes'
55 pushConstant: 'No'
56 send: ifTrue:ifFalse:
57 returnTop


(2 > 3) ifTrue: ['Yes'] ifFalse: ['No']

49 pushConstant: 2
51 pushConstant: 3
53 send: >
54 jumpFalse: 57
55 pushConstant: 'Yes'
56 jumpTo: 58
57 pushConstant: 'No'
58 returnTop

Thanks,
Jaromir







>
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