[catnaroek]

> There is an implementation of the Ruby language called Rubinius that statically looks at the instance variables in a class that are visible in the source code, and optimises the objects for that many instance variables. If you start to set extra variables dynamically, and so upset this static analysis, performance drops by a half.

You can implement an unsound static analysis for any language, and this in fact what Rubinius is doing: it's making potentially wrong conclusions about what instance variables will exist in objects. However, unsound analyses are outright harmful:

(0) Undoing unsound “optimizations” costs even more performance than was supposed to be gained by optimizing your program. (As you found out the hard way yourself.)

(1) They lie to you about what your code means! If this isn't bad enough, I don't know what else could be.

Unfortunately, a sound static analysis of Ruby code wouldn't be able to tell you much, precisely because Ruby allows you to subvert everything at runtime.

[chrisseaton]

> As you found out the hard way yourself.

That makes it sound like I implemented it - I didn't - I implemented the alternative mechanism which doesn't have the same problem.