From: Robert Klemme <shortcutter@...>
Date: 2011-03-13T22:20:35+09:00
Subject: Re: send() with a block?

On 12.03.2011 22:50, Sean O'Halpin wrote:
> On Sat, Mar 12, 2011 at 9:11 PM, Peter Zotov<whitequark@whitequark.org>  wrote:
>> On Sun, 13 Mar 2011 06:01:31 +0900, Sean O'Halpin wrote:
>>>
>>> On Sat, Mar 12, 2011 at 8:45 PM, 7stud --<bbxx789_05ss@yahoo.com>  wrote:
>>>>
>>>> Why don't the ruby docs say that send() can take a block?
>>>>
>>>> Kernel.send(:define_method, :my_meth) do |x|
>>>>   puts x
>>>> end
>>>>
>>>
>>> It's not the send() that's consuming the block - it's the define_method().
>>>
>>
>> But send() still bothers to pass the block around. Consider the following
>> code:
>>
>> ---8<---8<---
>> def my_method
>>   p block_given?
>> end
>>
>> def my_send # imitating send
>>   my_method
>> end
>>
>> my_send # =>  false
>> ---8<---8<---
>>
>> --
>>   WBR, Peter Zotov.
>>
>>
>
> I'm not sure what you're showing me here. But consider this:
>
> class Foo
>    def self.send(*a,&block)
>      p block_given?
>      super(*a)
>    end
> end
>
> class Bar
>    def self.send(*a)
>      p block_given?
>      super(*a)
>    end
> end
>
> Foo.send(:define_method, :my_method) do |x|
>    p x
> end
>
> block = proc{ |x| p x }
> Bar.send(:define_method, :my_method2,&block)
>
> foo = Foo.new
> foo.my_method(1)
> bar = Bar.new
> bar.my_method2(2)
>
> def my_method(x)
>    p x
> end
>
> my_method(10,&block)
>
> __END__
> true
> true
> 1
> 2
> 10
>
> Even when you explicitly do /not/ pass on the block (as in the
> super(*a) call above), send() does not consume it.

Automatic propagation of the block is not a feature of #send but a 
feature of "super":

 >> class X
 >> def a;p block_given? end
 >> def b;p block_given?;a end
 >> def c;p block_given?;send(:a) end
 >> end
=> nil
 >> X.new.a {1+2}
true
=> true
 >> X.new.b {1+2}
true
false
=> false
 >> X.new.c {1+2}
true
false
=> false


 >> class A
 >> def a;p block_given? end
 >> end
=> nil
 >> class B < A
 >> def a;p block_given?;super end
 >> end
=> nil
 >> class C < A
 >> def a;p block_given?;super() end
 >> end
=> nil
 >> A.new.a {1+2}
true
=> true
 >> B.new.a {1+2}
true
true
=> true
 >> C.new.a {1+2}
true
true
=> true

> Passing a block using the&block syntax is simply part of ruby's
> method calling syntax.
> A method does not have to specify that it takes a block for you to
> call it with one.

Correct.

Kind regards

	robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/