From: Robert Klemme <shortcutter@...>
Date: 2011-01-18T17:02:20+09:00
Subject: Re: Why Ruby Does Not Support Method Overloading?

On Tue, Jan 18, 2011 at 2:09 AM, Su Zhang <zhangsu@live.com> wrote:
> From my understanding, taking the number of arguments, runtime type of
> arguments or even the formal parameter names into account for message to
> method mapping will complicate the language implementation.

... and method lookup tables will potentially be larger.  Dunno
whether this is a critical factor though.

> This is also
> the reason why Ruby does not support multiple dispatch at the language
> level. Common-Lisp does support multiple dispatch, but it does so by
> including a type modifier to the arguments so that they can be checked
> against the actual runtime type of arguments, which, IMO, is as
> unpleasant as doing something like the following in a single method
> definition:
>
> case arg
> when String
>    # ...
> when Symbol
>    # ...
> end

For multiple arguments the unpleasant variant looks like this (1.9 and later):

def f(*args)
  case args.map(&:class)
  when [Array, Array]
    puts "Array * 2"
  when [String, Array]
    puts "String, Array"
  when [Hash]
    puts "Hash"
  else
    raise ArgumentError, "Don't know what to do with %p" % [args]
  end
end

Cheers

robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/