From: Brian Candler <B.Candler@...>
Date: 2007-09-06T17:17:11+09:00
Subject: Named argument passing, and method_args extension

Quick question - what are the current thoughts about named argument passing
in future versions of Ruby? I've seen it requested in the past but not much
in the way of concrete proposals.

Those awfully nice Merb people have just come up with a clever idea, already
implemented as a small C extension. This lets you reflect on the names of
arguments in a method definition.

  require 'method_args'
  class X
    def hello(foo, bar)
      nil
    end
  end

  x = X.new
  meth = x.method(:hello)
  meth.args? # => true
  meth.args  # => ['foo', 'bar']        <<< cool!

This has been released as a Gem, see
http://rubyforge.org/pipermail/merb-devel/2007-September/000239.html

The idea is that instead of writing

  def show
    id = params[:id]
    page = params[:page]
    ...
  end

you should be able to write

  def show(id, page=nil)
    ...
  end

with Method#args allowing the desired elements of the params hash to be
picked out automatically and passed in the correct order.

Effectively what you end up is something like a splat call, but with the
arguments in named order as defined by the method definition.

Taking this one step further, has it been considered that splat might be
applied to a hash in the same way? e.g.

   def func(a, b, c)
     [a, b, c]
   end

   func( *{:c=>3, :b=>2, :a=>1} )  # => [1,2,3]   :-)

I had a look at http://eigenclass.org/hiki.rb?Changes+in+Ruby+1.9#l4 but
couldn't see anything along these lines.

In 1.8, splat _does_ work on a hash, but only by flattening it to an array
first, which isn't very useful as the order is arbitary.

irb(main):003:0> def f(*a); p a; end
=> nil
irb(main):004:0> f(*[1,2,3])
[1, 2, 3]
=> nil
irb(main):005:0> f(*{:a=>1,:b=>2})
[[:b, 2], [:a, 1]]
=> nil

Regards,

Brian.

P.S. By symmetry, I'd suggest that any 'unused' elements could be available
as a hash too:

  def func(a, b, c=3, *d)
    p a, b, c, d
  end

  func( *{:a=>1, :b=>2, :e=>5, :f=>6} )
  # 1
  # 2
  # 3
  # {:e=>5, :f=>6}

However this does mean that the receiver of *d would have to be able to cope
with receiving either an Array or a Hash.