From: Yossef Mendelssohn <ymendel@...>
Date: 2010-09-04T00:40:01+09:00
Subject: Re: Enumerator#each return value is surprising



On Sep 3, 10:12 am, Christopher Dicely <cmdic...@gmail.com> wrote:
> I suppose when the enumerator is created with the default options, I
> can sort of see that (or at least, see it as unlikely to be harmful.)
> When its created with enum_for with an argument other than :each,
> though, it seems to me like you end up with more possibility for
> unexpected results.
>
> e.g.,
>
> array = ["a","b","c"]
> enum = array.enum_for(:each_with_index)
> enum.each {} # => ["a","b","c"]
> enum.to_a.each {} # => [["a", 0], ["b", 1], ["c", 2]]
>
> That is, even ignoring the implementation class, the sequence returned
> by Enumerator#each isn't always the same sequence that the Enumerator
> represents. This isn't like any other Enumerable in core Ruby.

First system ruby 1.8.6, then rvm with 1.9.1

$ irb
>> %w[a b c].each {}
=> ["a", "b", "c"]
>> %w[a b c].each_with_index {}
=> ["a", "b", "c"]
>> exit

$ rvm use ruby-1.9.1
$ irb
>> %w[a b c].each
 => #<Enumerator:0x48cc30>
>> _.each {}
 => ["a", "b", "c"]
> %w[a b c].each {}
 => ["a", "b", "c"]
> %w[a b c].each_with_index {}
 => ["a", "b", "c"]
> %w[a b c].each_with_index
 => #<Enumerator:0x47f2f8>
> _.each {}
 => ["a", "b", "c"]

You should learn to expect the original array as a return value. It's
not about what kind of `each` enumeration you use, but the ability to
chain calls as expected. If you want to get something different, use a
transforming enumerator instead of `each`.

--
-yossef