From: Benoit Daloze <eregontp@...>
Date: 2010-03-01T03:53:17+09:00
Subject: Array#join using to_a if defined

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Hi,

I got recently an unexpected result using Array#join.

In my thoughts, Array#join is sth like adding the separator between every
element#to_s.

That is what seems to happen when there is no any #to_a method defined in an
element:

For example,
class N < Struct.new(:n)
  def to_s
    'to_s'
  end
end

[N.new(2), N.new(3)].join(' ') #=> "2 3" and not "to_s to_s"

This is due to Struct::new that defines #to_a that return an Array of
instance variables (here :n).
That's quite annoying, because you would expect when you're defining to_s to
be the only usual String representation.
The only way to edit that behavior without changing Array#join, is to
"undef_method :to_a", not very nice ...
or to use ary.map(&:to_s).join, very redundant.

Shouldn't Array#join looks like:
class Array
  def join(sep = $,)
    sep = '' if sep.nil?
    s = ""
    self.each_with_index { |e, i|
      s << e.to_s
      s << sep unless i == size-1
    }
    s
  end
end

Why is it this 'look' to element#to_a ? is that really interesting? when?
Maybe when you use [[1],[2,3]].join #=> "123" ? Then we should look for
#to_ary, not #to_a

Regards,
B.D.

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