From: Roger Pack <rogerpack2005@...>
Date: 2008-07-06T14:04:13+09:00
Subject: Re: Faking named parameters and enforcing required params

Greg Willits wrote:
> I come from years of using a language with named params. I prefer the
> explicitness of it, so I'm tending to do a lot of it in my Ruby code
> using a hash to fake it
> 
>   object.method(:shape=>'square', :size='medium')
> 
> What I am wondering is whether there's an idiomatc preference to dealing
> with the hash inside the method?
>   object->task(-shape='square', -size='large') # legal
>   object->task(-shape='square') # legal
>   object->task(-size='medium') # failed for lack of required param
> 
> The required and optional features combined with some other stuff got
> very close to a full design by contract implementation.

Interestingly, I have also been working on something very similar to 
this recently. [a named parameter parser for ruby]


Basically it parses an array as a parameter list, with some required and 
some optional parameters.
ex:

[first remember that you can pass parameters to a method via * for a 
variable number of parameters, i.e. def method *args; end passes in args 
as an array of all parameters]

the syntax it uses is:

def method1 *as
  required1, required2, optional1 = as.args [:required1, :required2], 
{:optional1 => 3}
end

and you call it either named or unnamedly, a la:
method1 4, 5, 6
or
method1 4, 5
or
method1 :required1 => 1, :required2 => 2
or
method1 :required1 => 1, :required2 => 2, :optional1 => 4
or
method1 1, 2, :optional1 => 4
whichever floats your boat.

Try it out, let me know if it works.

the file is

http://code.google.com/p/ruby-roger-useful-functions/source/browse/trunk/arg_parser/enhanced_arg_parser.rb

and docs for it http://wilkboardonline.com/roger/arg_parser/doc/ [see 
args method for description].
Thanks!

-R
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