須藤です。

> +    if (NIL_P(size) || size == Qundef) {
> +	ary = rb_ary_new();
> +    }
> +    else {
> +	ary = rb_ary_new_capa(NUM2LONG(size));
> +    }

を

    if (FIXNUM_P(size)) {
	ary = rb_ary_new_capa(NUM2LONG(size));
    }
    else {
	ary = rb_ary_new();
    }

とかsizeが返す値が数値じゃなかったらこれまでと同じ挙動にする
ようにしてもらえないでしょうか?

これまでは

class NonIntegerSizeEnum
  include Enumerable

  def initialize(n)
    @n = n
  end

  def each
    @n.times { |i| yield i }
  end

  def size
    :size
  end
end

NonIntegerSizeEnum.new(100).to_a

というコードが動いていたんですが、この変更の後からは

/tmp/b.rb:17:in `to_a': no implicit conversion of Symbol into Integer (TypeError)

というエラーがでるようになってしまって困っています。

In <20150510022540.1547A118611 / sakura2.atdot.net>
  "[ruby-changes:38376] glass:r50457 (trunk): * enum.c (enum_to_a): Use size to set array capa when possible." on Sun, 10 May 2015 11:25:40 +0900 (JST),
  glass <ko1 / atdot.net> wrote:

> glass	2015-05-10 11:25:33 +0900 (Sun, 10 May 2015)
> 
>   New Revision: 50457
> 
>   http://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=50457
> 
>   Log:
>     * enum.c (enum_to_a): Use size to set array capa when possible.
>       the patch is from HonoreDB <aweiner at mdsol.com>.
>       [fix GH-444]
> 
>   Modified files:
>     trunk/ChangeLog
>     trunk/enum.c
> Index: ChangeLog
> ===================================================================
> --- ChangeLog	(revision 50456)
> +++ ChangeLog	(revision 50457)
> @@ -1,3 +1,9 @@ https://github.com/ruby/ruby/blob/trunk/ChangeLog#L1
> +Sun May 10 11:23:03 2015  Masaki Matsushita <glass.saga / gmail.com>
> +
> +	* enum.c (enum_to_a): Use size to set array capa when possible.
> +	  the patch is from HonoreDB <aweiner at mdsol.com>.
> +	  [fix GH-444]
> +
>  Sat May  9 06:48:36 2015  Eric Wong  <e / 80x24.org>
>  
>  	* ext/socket/ancdata.c (bsock_recvmsg_internal): GC guard
> Index: enum.c
> ===================================================================
> --- enum.c	(revision 50456)
> +++ enum.c	(revision 50457)
> @@ -515,7 +515,14 @@ enum_flat_map(VALUE obj) https://github.com/ruby/ruby/blob/trunk/enum.c#L515
>  static VALUE
>  enum_to_a(int argc, VALUE *argv, VALUE obj)
>  {
> -    VALUE ary = rb_ary_new();
> +    VALUE ary, size = rb_check_funcall(obj, id_size, 0, 0);
> +
> +    if (NIL_P(size) || size == Qundef) {
> +	ary = rb_ary_new();
> +    }
> +    else {
> +	ary = rb_ary_new_capa(NUM2LONG(size));
> +    }
>  
>      rb_block_call(obj, id_each, argc, argv, collect_all, ary);
>      OBJ_INFECT(ary, obj);
> 
> --
> ML: ruby-changes / quickml.atdot.net
> Info: http://www.atdot.net/~ko1/quickml/