From: Greg Willits <lists@...>
Date: 2008-06-24T15:12:25+09:00
Subject: Faking named parameters and enforcing required params

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?

Currently, I just do the prozaic:

  def task(parameters)
    shape = parameters[:shape]
    size = parameters[:size]

Should I be doing something else?

In that other language (Lasso), it also offered a way to declare
required and optional parameters

  define_tag:'task',
    -required = 'shape',
    -optional = 'size';

    ...blah...

  /define_tag;

which then got used like this:

  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.

Anyway, I figured out I could simulate the assignment side of required
and optional with this:

  def task(parameters)
    @shape = parameters[:shape]
    @size = parameters[:size] ||= 'medium'

What I have't figured out is an elegant pattern in Ruby for enforcing
required  parameters -- other than a bunch of hand written exception
coding.

To summarize my questions:

A) is there something better than x = parameters[:x]?
B) if :x isn't in (parameters), what's the best way to complain to the
developer about that?

Many thanks.

-- gw
-- 
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