[ruby-core:18144] Re: Enumerators that know about a block

Hi --

On Wed, 6 Aug 2008, Shugo Maeda wrote:

> Hi,
>
> 2008/8/6 David A. Black <[e-mail]>:
>>> 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.
>
> It's just a hypothetical example.  Enumerator can't do that automatically,
> because Enumerable#map is implemented to produce Array.
>
> If you don't mind memory consumption, you can write like this:
>
>  e = [1, 2, 3].map {|x| x * 10}.each
>  p e.next #=> 10
>  p e.next #=> 20

I'd rather have an enumerator that already knows both the method it
represents and the block it's supposed to use. I guess I got used to
it when we had:

   e = array.enum_for(:map, &block)

and I never understood why that was removed. I think it's someone
else's "least surprise" :-)


David

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