From: Robert Klemme <bob.news@...>
Date: 2005-06-29T19:05:42+09:00
Subject: Re: yield does not take a block

Eric Mahurin wrote:
> --- Yukihiro Matsumoto <matz@ruby-lang.org> wrote:
>
>> Hi,
>>
>> In message "Re: yield does not take a block"
>>     on Wed, 29 Jun 2005 02:30:05 +0900, Daniel Brockman
>> <daniel@brockman.se> writes:
>>
>>> I feel strange when I see these are not equivalent:
>>>
>>>  def foo1 &block
>>>    block.call &bar
>>>  end
>>>
>>>  def foo2
>>>    Proc.new.call &bar
>>>  end
>>>
>>>  def foo3 &block
>>>    yield &bar
>>>  end
>>
>>> If foo1 and foo3 are not equivalent, then we have an inconsistency.
>>
>> Indeed we have inconsistency here if those two are not
>> equivalent, but
>> I don't think consistency matters most in this case.  Using
>> yield
>> emphasizes passing a value and control to a block given to
>> the method.
>> On the other hand, "call"ing an block argument (&block)
>> emphasizes
>> treating a block as a procedural object.  If they are
>> focusing
>> different aspect, they might not be exact same.
>>
>> It's not a technical issue.  Just a matter of how we feel
>> when we see
>>
>>   yield &bar
>>
>> or
>>
>>   yield {...}
>>
>> I feel something strange (bad strange) when I see this, just
>> because
>> it passes a block to another block, which is apparently
>> strange,
>> whereas
>>
>>   block.call &bar
>>
>> does not make me feel bad strange, since it is valid syntax
>> in the
>> microscopic view, even when it is semantically strange.
>>
>> If you have shown me the reason "yield &bar" is not strange
>> (and is
>> useful) other than consistency, I'd be glad to apply the
>> Nobu's patch
>> in [ruby-talk:146636].
>>
>> matz.
>
>
> I tend to agree that the yield should be made consistent with
> block.call such that yield would basically be just an alias for
> block.call (where block is the block given to the current
> method).  I think any keyword that can reasonably be made to
> look like a method call, should.  Makes the syntax more
> consistent.  If you were starting over, I'd even suggest things
> like if/while to be like (or actually) method calls.
>
> but...
>
> Personally, I don't think having yield as a keyword really adds
> that much value to the language.  The only advantages I see
> over explicitly having a &block arg and using block.call are a)
> it looks like smalltalk, and b) rdoc parses it better.  I think
> showing the &block on the def line makes the method interface
> clearer up front.  I don't use yield at all and haven't missed
> it.

Note though that yield and &c.call work quite differently.  This has for
example performance implications.

Kind regards

    robert