From: Yukihiro Matsumoto <matz@...>
Date: 2005-10-22T12:12:05+09:00
Subject: Re: A comparison by example of keyword argument styles

Hi,

In message "Re: A comparison by example of keyword argument styles"
    on Sat, 22 Oct 2005 00:44:58 +0900, Daniel Berger <Daniel.Berger@qwest.com> writes:

|>   def foo(*args)
|>     # how do you delegate arguments?
|>     bar(*args)
|>   end
|> 
|>   def bar(a,b,c)
|>     p [a,b,c]
|>   end
|> 
|>   foo(1,a:2,c:3)
|
|Not allowed because redefinition of the same parameter raises an error.  Here 
|you're trying to define 'a' twice, once as the first positional argument, once 
|as a named parameter.

Then what if foo(1,b:2,c:3) ?

|Yes, it's uglier.  How does it work in your implementation? I'm curious to know 
|how you preserve argument order.

For mine, args in foo becomes [1,{:a=>2,:c=>3}].  And suppose

  def bar(a:,b:,c:)
    p [a,b,c]
  end

since it requires explicit keyword arguments, delegation should be
plain 

  bar(*args)

and bar prints [1,2,3].

|Let me ask you the same thing.  What happens here with your implementation?
|
|class Foo
|    def foo(a:, b:, c:)
|       p [a,b,c]
|    end
|end
|
|class Bar < Foo
|    def foo(d:, e:, f:)
|       super
|    end
|end
|
|Bar.new.foo(f:3, e:2, d:1)

Bar#foo receives [{:f=>3,:e=>2,:d=>1}], then it delegates arguments to
Foo#foo.  Foo#foo accepts keyword arguments a, b, c, and no other
keywords (it does not have ** in the list), it raises ArgumentError.

							matz.