An Untyped Calculus of Aspect-Oriented Programs

Radha Jagadeesan

Alan Jeffrey

James Riely

DEPAUL UNIVERSITY, CHICAGO

Aspect Oriented Programming

AOSD. Systematic methodology to address cross-cutting concerns

A standard example: logging AOP. Language support to ``localize’’

cross cutting code This talk. About AOP languages

Specification via translation

Weaving: describe operational semantics of a AOP language via compilation to the underlying paradigm.

Aspect + Java ! Java Aspect + Scheme ! Scheme Aspect + ML ! ML Aspect + C ! C

AOP languages and OO languages: Folklore

Execution in OO languages is an instance of execution in AOP languages

Translation from OO programs P

to AOP program Pasp

P1 ! P2 , P1asp

! P2asp

AOP languages and OO languages: Folklore

Execution in OO languages is an instance of execution in AOP languages

Aspects interfere with OO principles

Aspects interfere with OO programming

D1, D2 are distinguishable.

Aspects as first class entities?

Source semantics is non-trivial. Aspects + OO: redundancy Aspects interfere with OO principles

Rest of the talk

Overview of results

A sketch of the technical development

A calculus of AO programs

Identify a core set of orthogonal primitives

Only AROUND advice

No method bodies

Only call/execution pointcuts

Direct description of the operational semantics of aspect based programs

So what?

Dynamic arrival of new advice permitted.

Specification of weaving

No reductions are lost No new reductions

Limitations

Limited vocabulary of pointcuts.

Only call/execution join points

Reflection, cflow not included

Global specification of advice order

Rest of this talk: A sketch of the main ideas

An overview of call vs. execution The aspect calculus Weaving

An Advised Method call

o:C

u:D

u.foo()a

proceed()

o.foo(u)

An Advised Method call

o:C

u:D

u.foo()a

proceed()

o.foo(u)

Call advice

Executed in the controlling context of the caller

An Advised Method call

o:C

u:D

u.foo()a

proceed()

o.foo(u)

Execution advice

Executed in the controlling context of the callee

Rest of this talk

An overview of call vs.. execution The aspect calculus Weaving

The Aspect Calculus

Class declarations

Pointcuts Advice

The Aspect Calculus: Classes

Class = list of method names

Methods have no code

The Aspect Calculus: Pointcuts

The Aspect Calculus: Advice

Given fixed global ordering on advice names

Reduction rules: context

Reduction rules: fetching advice

Keep track of controlling object p{…}

Call advice determined by static type. Execution advice determined by dynamic type

Reduction rules: call advice

Controlling context of caller p

Substitutions for this, target proceed, parameters

Reduction rules: execution advice

Controlling context of callee o

Substitutions for this, target proceed, parameters

Encoding Class Based Language 1

Create an exec advice for each method body

Encoding Class Based Language 2

proceed

cbl_d_m cbl_c_m

Name cbl_d_m precedes name cbl_c_m in ordering on advice names

Rest of this talk

An overview of call vs. execution The aspect calculus Weaving

Weaving

Programs that dynamically load advice affecting existing classes cannot be woven statically.

For static advice, weaving algorithm is (by now)standard.

Novelty is specification of weaving.

Weaving: Basic idea

View as a kind of macro-expansion.

To weave

Weave recursively

and associate result to the body of method m

Weaving

Alas. This doesn’t necessarily terminate.

However, postpone macro-expansion to runtime by freezing inside method bodies.

Formalized in paper.

A subtlety in correctness proof

Weaving of intermediate configurations requires knowledge of controlling object

Rest of this talk

An overview of call vs. execution The aspect calculus Weaving Summary

This talk: A calculus of AOP programs

Identify a core set of orthogonal primitives

Direct description of the execution of programs in an aspect language.

Moving along

Scale: Larger variety of pointcuts.

Accurate treatment of advice order.

Source level typing