From: Robert Klemme <bob.news@...>
Date: 2005-12-31T22:02:56+09:00
Subject: Re: Optional arguments and default values

Ross Bamford <rosco@roscopeco.remove.co.uk> wrote:
> On Fri, 30 Dec 2005 19:59:05 -0000, Surgeon <biyokuantum@gmail.com>
> wrote:
>> Hi,
>>
>> How do I give a method optional arguments and default values?
>>
>> Exmpl:
>>
>> foo is a function that multiplies all of its arguments together. If
>> there is not any argument, a default value of "qwerty" returns.
>>
>> foo(2,3)    ---->  6
>> foo(2,3,5) ----> 30
>> foo(2,3,5,2) -> 60
>>
>> foo() -----------> "qwerty"
>>
>
> Maybe:
> def foo(*args)
>   args.empty? && "qwerty" or args.inject(0) { |s,i| s * i }
> end
>
> or:
>
> def foo(*args)
>   if args.empty?
>     "qwerty"
>   else
>     args.inject(0) { |s,i| s * i }
>   end
> end

The implementation of Enumerable#inject allows for an even more elegant 
solution

def foo(*args)
  args.inject {|a,b| a*b} || "qwerty"
end

>> foo 2,3,5
=> 30
>> foo 2,3
=> 6
>> foo 2
=> 2
>> foo
=> "qwerty"

Note: if args is empty this inject returns nil, if there is just one element 
that is returned.

Another solution would be to implement things like this in Enumerable:

module Enumerable
  def sum()     inject(0) {|a,b| a+b} end
  def product() inject(1) {|a,b| a*b} end
end

or

module Enumerable
  def sum()     inject {|a,b| a+b} end
  def product() inject {|a,b| a*b} end
end

Allowing for invocations like these

>> [1,2,3,4].sum
=> 10
>> (1..4).sum
=> 10
>> (1...5).sum
=> 10
>> (1..10).map { rand 20 }.sum
=> 91

Kind regards

    robert