From: 7stud -- <bbxx789_05ss@...>
Date: 2007-11-01T03:52:31+09:00
Subject: Re: .each do |foo, bar| what does bar do?

David A. Black wrote:
> Hi --
> 
> On Sun, 28 Oct 2007, 7stud -- wrote:
> 
>>> class Hash
>>>   def each
>>>     each_key {|key| yield key, self[key] }
>>>   end
>>> end
>>>
>>
>>
>> That suffers the same problem as David Black's example.
> 
> What problem did mine suffer from?
> 

It doesn't return an array.

>def each(&block)
>   orig_each(&block)
>
> versus
>
>>    orig_each(block)
>>
>> According to pickaxe2, p56, the '&' method converts the specified block
>> to a Proc object and assigns it to the parameter variable 'block'.  Why
>> is the second call to '&' required?
> 
> Because there's a difference between passing a Proc around as an
> object, and supplying a code block to a method. You can do both:
> 
>    meth(arg,&block)
> 
> and arg can be a Proc object. So there has to be some way to tell the
> method what you're doing.
> 

I'm not getting it.  With this definition:

def each(&a_block)

when I call:

each() {some block}

ruby converts the block to a Proc object and assigns it to the variable 
a_block.  So, it seems to me that after ruby passes the args specified 
in the method call to each(), the block would no longer be accessible 
inside the method--only the Proc object assigned to a_block would be 
accessible.  Are you saying that when the next line executes:

>def each(&a_block)
>   orig_each(&a_block)  <----****

that the parameter variable a_block in the line:

> orig_each(&a_block)

is not the same variable as the a_block in the line:

> def each(&a_block)

????  In other words, does a_block in the line:


> orig_each(&a_block) 


reach outside the method definition and reference the block that is 
floating around in the ether?  Does ruby re-convert the block into a 
Proc object and re-assigns the Proc object to a_block?  If not, I don't 
understand why the second '&' is necessary: writing a_block should be 
enough to access the Proc object that ruby assigned to the parameter 
variable a_block when the method was first called.




-- 
Posted via http://www.ruby-forum.com/.