From: Eleanor McHugh <eleanor@...>
Date: 2007-04-04T19:36:00+09:00
Subject: Re: Everything is a object?

On 4 Apr 2007, at 11:02, Jamal Soueidan wrote:
> I have been reading about these various boolean returns, how Ruby look
> at them, as you mentioned false and nil is the only objects which are
> considered false.
>
> But I thought you did not need to define/declare any variables before
> using it, but this has been misunderstood, you should somehow  
> assign the
> variable to something before trying to use it, since Ruby "Still"  
> don't
> know what object it is, right?

The point is that you don't have to define a variable before you make  
an assignment to it, much like in older variants of BASIC. Assignment  
implicitly declares the variable to exist within the specified scope.  
However until you make an assignment the interpreter is not aware of  
the variable's existence (because logically it does not yet exist)  
and so attempts to reference it will fail to produce a reference to  
an object. An attempt will also be made to apply the token to the  
current object as a method, and if this too fails then the  
interpreter has no choice but to flag an error condition because  
semantically your program is broken - it makes no sense.

When you use defined? all you are essentially doing is asking the  
interpreter whether or not the given token references an object  
within the current scope.

Whilst the interpreter could be implemented in such a way that every  
unknown token returned a nil object if it was unknown to the  
interpreter, this would break the principle of least surprise. Think  
of this as equivalent to NaN (not a number) in standard floating- 
point libraries.


Ellie

Eleanor McHugh
Games With Brains
----
raise ArgumentError unless @reality.responds_to? :reason