From: Jamis Buck <jgb3@...>
Date: 2004-11-06T00:33:58+09:00
Subject: Re: value provided for argument with default value - how to check inside method?

itsme213 wrote:
> "Robert Klemme" <bob.news@gmx.net> wrote
> 
>>I'm unsure what you're at.  Normally the idea of having a default value is
>>that you don't have to worry about where it came from:
>>
>>def foo(x=10)
>>  puts x
>>end
>>
>>Care to unveil a bit more detail why you would need that piece of
>>information?
> 
> 
> In this case, I want to use foo() and foo(x) as getter and setter
> respectively i.e. some form of overloading.

You can always do something like the following. Create a constant and 
initialize it to a unique object instance. Then, use that instance as 
the default value to your method:

   VALUE_NOT_SPECIFIED = Object.new
   def foo( x = VALUE_NOT_SPECIFIED )
     case x
       when VALUE_NOT_SPECIFIED
         @x
       else
         @x = x
     end
   end

Of course, someone could still explicitly pass the argument 
VALUE_NOT_SPECIFIED to the method, but then they would obviously be 
trying pretty hard to do what they aren't supposed to do...

- Jamis

-- 
Jamis Buck
jgb3@email.byu.edu
http://www.jamisbuck.org/jamis