From: Josh Cheek <josh.cheek@...>
Date: 2010-12-29T22:21:49+09:00
Subject: Re: What am I missing about splat operator?

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On Tue, Dec 28, 2010 at 9:12 PM, Ryan Davis <ryand-ruby@zenspider.com>wrote:

>
> # 2
> pet1, pet2, pet3 = ["duck","dog","cat"] # no splat operator
>
> #   # 2
> #   s(:masgn,
> #     s(:array, s(:lasgn, :pet1), s(:lasgn, :pet2), s(:lasgn, :pet3)),
> #     s(:to_ary, s(:array, s(:str, "duck"), s(:str, "dog"), s(:str,
> "cat")))),
>
>
This implies to me that I should be able to define to_ary on an object, and
it will be able to be RHS of a mass assign.

a = Object.new

def a.to_ary
  [1, 2]
end

b , c = a

b # => 1
c # => 2


Yes, it works. But I am confused where to_ary came from. I have never used
it myself, and wouldn't have even thought to use it except I saw it in the
sexp. Googling turns up http://www.ruby-forum.com/topic/81642, which isn't
helpful, and http://forums.pragprog.com/forums/54/topics/992 which left me
rather unconvinced, and only addresses the difference without really
addressing the reasoning.



Same for the Pickaxe which says on 366
to_ary: "This is used when interpreter needs a parameter to a method to be
an array, and when expanding parameters and assignments containing the *xyz
syntax"
to_a: "This is used when the interpreter needs to convert an object into an
array for parameter passing or multiple assignment."
So one's a po-tay-to, the other's a po-tah-to?



In The Ruby Programming Language, on page 80, it says they are defined for
the purposes of implicit conversions. I verified with this code

class Fixnum
  alias to_str to_s
end
'1' + 1 # => "11"

But I don't understand why the implicit version should be different from the
explicit version, or why "#{obj}" doesn't invoke the implicit version. Is
there some example which shows the necessity of a separate, but but similar
method for to_a/to_ary, to_i/to_int, to_s/to_str, etc?

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