tag semantics

A Subtle Change to Mixin Semantics in Ruby 1.9

Posted by Rick DeNatale Mon, 09 Oct 2006 20:07:00 GMT

I’ve been working on a little tool to peek behind the curtain and see a bit of what’s going on behind the scenes in the standard Ruby implementation (i.e ‘ruby’ as opposed to ‘Ruby’)

While doing this I was looking at the code which ruby runs when you include a module in a class or another module. I noticed that ruby 1.8 was going to some pains not to move the proxy for an included module in the inheritance chain.

To verify what my eyes seemed to be telling me, I wrote a silly little test program which created a module with one method, and several classes.

This test verified my reading of the 1.8 code. I then tried the same test using the latest ruby 1.9 and found that module mixin semantics have changed.

Read on

On Variables, Values, and Objects

Posted by Rick DeNatale Wed, 13 Sep 2006 19:47:00 GMT

I’ve recently observed some posts to ruby-talk which evidence some confusion on the part of the posters about the relationship between variables and objects in Ruby. One currently active thread concerns several participants who are upset that instances of the Matrix class in the Ruby standard library can’t be changed once created.

In Ruby, like in other uniformly object-oriented languages, the relationship between variables and their values is subtly different than in other languages, and this is a crucial paradigm shift, which must be crossed in order to understand Ruby.

In many languages a variable names an area in memory which holds a “bag-of-bits” representing the value of the variable. The size of that area depends on the type of the variable. A variable holding an integer might be 4-bytes long, while one holding a particular structure might be 325 (or whatever) bytes.

In a uniformly object-oriented language, all variables reference objects, and any variable can reference any object, or different objects over time. My good friend at IBM, the late David N. Smith, used to say that in such a language, “all variables are the same size,” when he wrote about or taught Smalltalk.

This distinction can trip up the unwary. Let’s try to clear some of the stumbling blocks out of the way.