[ruby-dev:34606] Re: Array#mapがEnumeratorを返さない

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。
--
Nobuhiro IMAI <[e-mail]>
Key fingerprint = F39E D552 545D 7C64 D690  F644 5A15 746C BD8E 7106