[ruby-dev:34635] Re: Array#mapがEnumeratorを返さない

At Thu, 8 May 2008 08:52:57 +0900,
Nobuhiro IMAI wrote:
> いまいです。
>
> From: rubikitch_at_ruby-lang.org
> Date: Thu, 8 May 2008 04:32:52 +0900
>
> > Array#mapでブロックをつけない場合にEnumeratorを返しません。
> >
> > RUBY_VERSION                           # => "1.9.0"
> > [8,3,9].map                            # => #<Enumerable::Enumerator:0xb7aba718>
> > [8,3,9].map.with_index{|x,i| [x*x, i]} # => [[64, 0], [9, 1], [81, 2]]
> >
> > RUBY_VERSION                           # => "1.8.7"
> > [8,3,9].map                            # => [8, 3, 9]
> > [8,3,9].map.with_index{|x,i| [x*x, i]} # =>
> >
> > # ~> -:11: undefined method `with_index' for [8, 3, 9]:Array (NoMethodError)
>
> NEWS に注記がありますね。
>
> (...)
>     Return an enumerator if no block is given.
>
>     Note that #map and #collect still return an array unlike Ruby 1.9
>     to keep compatibility.
> (...)
>
> [8,3,9].enum_for(:map).with_index{|x,i| [x*x, i]}
>
> でしょうか。

[8,3,9].each_with_index.map { |x,i| [x*x, i] }

でもいいです。

--
Akinori MUSHA / http://akinori.org/