From: Ross Bamford <rossrt@...>
Date: 2006-05-28T19:26:04+09:00
Subject: Re: Crazy thought -- Rubyish type conversion?

On Sun, 2006-05-28 at 18:25 +0900, transfire@gmail.com wrote:
> Can this be done already?
> 
>   def foo(bar, baz, bur)
>      argsto :i, :str, :sym
>      # something
>    end
> 

Here's a naive implementation:

require 'facet/binding'

def argsto(*syms)
  Binding.of_caller do |b|
    lvs = b.local_variables
    lvs.each do |lv|
      break if syms.empty?
      type = syms.shift.to_s
      begin
        if type =~ /^[A-Z]/
          b[lv] = send(type, b[lv])
        else
          type = "to_#{type}"
          b[lv] = b[lv].send(type)
        end
      rescue NameError
        raise ArgumentError,"No coercion #{type} for #{b[lv].inspect}",
          caller[3..-1]
      rescue ArgumentError
        raise ArgumentError, $!.message, caller[3..-1]
      end
    end
  end
end

If you really need this kind of thing, it seems to work:

def ameth(foo, bar, baz, &blk)
  argsto(:Integer, :String, :sym)
  blk.call(foo, bar, baz)
end

ameth('10',100,'puts') { |*args| p args }
# => [10, "100", :puts]

The added bonus you don't get if you just use to_i and and so on:

ameth('10a',100,'puts') { |*args| p args }
-:28:in `ameth': invalid value for Integer: "10a" (ArgumentError)
        from -:32

It's not particularly smart or fast, though. 

-- 
Ross Bamford - rosco@roscopeco.REMOVE.co.uk