From: "David A. Black" <dblack@...>
Date: 2008-08-06T10:44:06+09:00
Subject: [ruby-core:18138] Re: Enumerators that know about a block

Hi --

On Wed, 6 Aug 2008, Shugo Maeda wrote:

> Hi,
>
> 2008/8/1 David A. Black <dblack@rubypal.com>:
>> I'm remembering that at one point it was possible to do this:
>>
>>  array = [1,2,3]
>>  func = lambda {|x| x * 10 }
>>  e = array.enum_for(:map, &func)
>>  e.next
>>  => 10
>>
>> But now the result is 1, because &func is ignored.
>>
>> I'm (a) puzzled by this, since it seems to me that enumerators are
>> much more useful if they can remember a block, and (b) wondering if
>> there's some similar replacement technique that I haven't managed to
>> figure out.
>
> enum_for is designed to apply a block for the specified method
> (Array#map in this case) by later Enumerator method calls, so it
> simply ignores a given block.
>
> You may need the lazy version of Enumerable#map that returns
> Enumerator instead of Array.
>
>  e = [1, 2, 3].lazy_map {|x| x * 10}
>  p e.next #=> 10
>  p e.next #=> 20

Is that an actual method (I couldn't find it anywhere) or just a
hypothetical example? I'm still wondering why enumerators aren't
designed to do that automatically if they're given a block upon
initialization.


David

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