From: "David A. Black" <dblack@...>
Date: 2007-11-01T07:15:01+09:00
Subject: Re: .each do |foo, bar| what does bar do?

Hi --

On Thu, 1 Nov 2007, 7stud -- wrote:

>> David A. Black wrote:
>>>>> That suffers the same problem as David Black's example.
>>>>
>>>> What problem did mine suffer from?
>>>>
>>>
>>> It doesn't return an array.
>>
>> Was it supposed to?
>>
>
> Hash#each returns an array(as my examples showed). You said:
>
>> If you were going to write Hash#each in Ruby, without recourse to
>> #each,
>
> So, yes...your example would have to return an array to implement
> Hash#each.

Actually Hash#each returns its receiver, which is a hash. I think my
code also returned self.

>
>> If you do this:
>>
>>    some_method(some_proc_object)
>>
>> you're just passing the Proc object around the same way you would pass
>> a string or an array or any other object.
>>
>> If you do this:
>>
>>    some_method &some_proc_object
>>
>> you're telling some_method that you want some_proc_object to play the
>> special role of code-block.
>>
>
> Ah.  So, it's like the splat operator(*)?  With the splat operator you
> might write:
>
> def meth1(*args)  #gathers the args into an array
>  meth2(*args)    #applied a second time -- explodes the array
> end
>
> def meth2(a, b)
>  p a
>  p b
> end
>
> meth1(1, 2)
>
> So, applying & a second time conceptually converts the Proc object back
> to a block and passes it to the method?

Yes. I wouldn't bother comparing it to the *. It's a way to use a Proc
object as a block. It doesn't have to be the one that was passed in
originally:

   def some_method
     p = Proc.new {|x| x * 10 }
     return [1,2,3].map(&p)
   end

>> There could even be a situation where you would do:
>>
>>    some_method(proc_1, proc_2) &proc_3
>>
>> i.e., send two procs as regular arguments, and use a third one as the
>> code block.
>>
>
> Whoa.  That doesn't seem consistent with your earlier example.  Why is
> proc3 outside the parentheses?  It doesn't seem to work:

Whoops, that was supposed to be inside, as your tests showed.


David

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