From: Devin Mullins <twifkak@...>
Date: 2007-04-05T09:42:28+09:00
Subject: Re: Everything is a object?

Jamal Soueidan wrote:
> I thought keywords are class, def, end, which mean something to the 
> compiler only.

http://www.google.com/search?q=ruby+keywords

The first result is comically direct.

> I did not think there would be something that behaved like a method 
> "defined?" which would be keyword?
> 
> Why not just make it a global method, put it in a module so nobody is 
> confused about that, because it looks like a method to me :)

The reason why not is that when calling methods, Ruby always evaluates 
the arguments first.[1] So saying `defined? blahblah` would fail, 
because Ruby would try to evaluate blahblah, not find a blahblah method, 
and raise a NoMethodError.

Now, you *could* make a defined method that took a String instead of a 
bare word, e.g.:
   def str_defined?(str) # cheap & ugly implementation
     eval "defined?(#{str})"
     # if you don't want to use defined? there are other hooks available:
     #  constants, local_variables, instance_variables, class_variables,
     #  global_variables
     # Those guys *are* methods, magically defined by the interpreter.
   end
   str_defined? "blahblah"

There are method/keyword parallels in Ruby like this -- define_method vs 
def, alias_method vs alias, etc.

You could even use blocks to make something that looked like:
   is_defined? { blahblah }
But that's very much insane.

 > Ruby already know whatever start with @ would be instance of
 > something, if not then it would still be nil object, means false.
"instance variable" does not mean "instance of something," but 
explaining what is *does* mean would mean a rather long side-wind into OOP.

 > Why does Ruby treat @myvar different from myvar?
BTW, you can emulate the @myvar way:
   def method_missing(sym, *a, &b)
     (!a.empty? || b) ? super : nil
   end

   a #=> nil
   a = 5
   a #=> 5

But, like, don't do that.

Devin

[1] This differs from other languages like Lisp and Io -- it probably 
comes from its C heritage.

> if a.nil?
>   p 'thanks';
> end

class You
   def self.method_missing(sym) puts "#{self}'re #{sym}." end
end
You.welcome