Dynamic Scope and Context-oriented Programming

or: Raising your Ruby shock-level with ContextR metaprogramming

(What is a shock-level?)

Dynamic Scope

Lexical Scope

History of Dynamic Scope

Semantics of Dynamic Scope

Comparision, side-by-side

Application of Dynamic Scope

STDIN etc.

Environment factors

Dissident

Implementation of Dynamic Scope

really: Dynamic Variables (explain why Scope is not really possible)

Show code!

How to in C (outline only)

Examples

Transition: Dynamically Scoping Methods

Context-oriented Programming

What is it?

What are layers good for?

Decoupling

Separation of concerns

Why?

good question, :-)

Because we can

Cool applications are possible (see later)

Excourse: Basics of method composition

AOP-like "salami tactic"

pre

post

wrap

Example

Example of COP with ContextR

Implementing ContextR

4 hours of hacking

this week :-)

Proof of concept, but no ugly hack

Implementing "salami tactic"

Limitations

&blocks and <1.9

Speed :/

Ideas for the future

Deoptimzation

Compilation

Caching

Hoping that YARV will make it a lot faster ;-)

Surprise, Surprise:

Implementing Namespace Selectors with pure Ruby (!)