[ruby-core:46730] Re: [ruby-trunk - Feature #6636][Open] Enumerable#size

Hello Marc-Andre

2012/7/24, marcandre (Marc-Andre Lafortune) <[e-mail]>:
>> * Enumerator.new(size) is not acceptable because of compatibility:
>>
>>   p Enumerator.new([1,2,3]).take(2)  #=> [1, 2]
>
> Agreed.
> I am proposing `Enumerator.new(size_lambda){ block }`, i.e. only if a block
> is given, then the first argument can be a lambda/proc that can lazily
> compute the size.

This is just my guess, but matz will not like such a method whose
meaning of its argument varies depending on whether block is given
or not.


> The old syntax of `Enumerator.new` without a block does not change meaning.

Is it okay that there is no way to specify size in this case?


>> * We cannot determine the size of enumerator when creating it:
>>
>>   a = [1]
>>   e = a.permutation
>>   a << 2
>>   p e.to_a  #=> [[1, 2], [2, 1]]
>>
>>   So, the API may need to receive a code fragment that calculates
>>   size, such as a Proc.
>
> Agreed.
> This is why I propose that `to_enum` accepts a block that can calculate the
> size, and Enumerator.new with a block can accept a lambda/proc for the
> same.

What argument(s) will the lambda/proc receive?

-- 
Yusuke Endoh <[e-mail]>