From: Ross Bamford <rossrt@...>
Date: 2006-05-02T09:53:06+09:00
Subject: Re: getting the name of arguments a method takes

On Tue, 2006-05-02 at 09:17 +0900, Dave Burt wrote:
> Guest wrote:
> > Didier Prophete wrote:
> >> I am wondering if there is a way to programatically get the name of the 
> >> arguments a function take.
> >>
> >> [...snip...]
> >>
> >> Is this even possible in ruby ?
> > 
> > i also would like to do this. anybody know if it's possible, and also
> > getting arg names from a proc? if so it would be very handy for
> > metaprogramming.
> 
> The short answer: no, it's not possible. What do you want it for?
> 
> There's always this way, though:
> 
> def method_arg_names(method_name, file)
>   File.read(file)[/def #{Regexp.escape method_name}(.*(\)|$))/, 1]
> end
> 
> p method_arg_names("method_arg_names", $0)  #=> "(method_name, file)"
> 
> Cheers,
> Dave

Also, this, if you're only dealing with Ruby methods and are in a
kamikaze kind of mood:

class Method
  def arg_names
    catch(:traced) do
      dummy_args = [nil]
      dummy_args *= self.arity unless self.arity < 0

      set_trace_func lambda { |event, file, line, id, bdng, cls|
        if event == 'call'
          set_trace_func nil
          throw(:traced, eval('local_variables',bdng).map { |lv| lv.intern })
        end
      }

      self.call(*dummy_args)

      # if we get here, call is bust
      set_trace_func nil
      raise "No ruby method call in block"
    end
  end
end

Doesn't work for procs, though.

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