The Meta in Meta-Object
Architectures
Marcus Denker, University of Bern
Mathieu Suen, INRIA
Stéphane Ducasse, INRIA
© Marcus Denker

Partial Behavioral Reflection
meta-object
links
activation
condition
source code
(AST)
Tanter, OOPSLA 2003
© Marcus Denker 2

Partial Behavioral Reflection
meta-object
links
activation
condition
source code
(AST)
David Röthlisberger, Marcus Denker and Éric Tanter:
Dynamic Unanticipated Partial Behavioral Reflection:
(Smalltalk) Adapting Applications at Runtime
Journal of Computer Languages, Systems and Structures, vol.
34, no. 2-3, July 2008, pp. 46-65.
© Marcus Denker 3

Partial Behavioral Reflection
meta-object
links
activation
condition
source code
(AST)
AST
Marcus Denker, Stéphane Ducasse, Adrian Lienhard
Philippe Marschall: Sub-Method Reflection
Journal of Object Technology, vol. 6, no. 9,
© Marcus Denker 4

Behavioral Reflection: Flexible
meta-object
links
activation
condition
source code
(AST)
> Very Flexible
© Marcus Denker 5

Behavioral Reflection: CLOS
meta-object
links
activation
condition
source code
(AST)
> Meta-class MOP (CLOS)
© Marcus Denker 6

Behavioral Reflection: AOP
meta-object
links
activation
condition
source code
(AST)
> Aspects
© Marcus Denker 7

Behavioral Reflection: Tracer
tracer metaobject
link
source code
(AST)
> Tracer
© Marcus Denker 8

Problem: Recursion
> Behavioral reflection cannot be applied to the whole
system
— System classes
— Meta-objects
© Marcus Denker 9

Example: Beeper
> Call the Beeper from OrderedCollection>>#add
beepLink := Link new metaObject: Beeper.
beepLink selector: #beep.
(OrderedCollection>>#add:) methodNode link: beepLink.
© Marcus Denker 10

Meta-object Call Recursion
Base Level Meta Object Meta Object
#add: send
#beep send
#add: send
#beep send
#add: send
Infinite recursion
© Marcus Denker 11

Ad-hoc Solutions
> Code duplication
> Adding special tests
© Marcus Denker 12

Tower of Interpreters
> Smith, 1982
© Marcus Denker 13

The Real Problem
Representing Meta-Level Execution
© Marcus Denker 14

The Meta-Context
Base Level Meta Level
MetaContext activation
> Link enables
MetaContext
MetaContext deactivation
© Marcus Denker 15

Context-aware Links
Base Level Meta Level
Stop meta-level call
> Disable call when
already on the
meta-level
© Marcus Denker 16

MetaContext
> Recursion problem solved meta-object
meta
links
level 0
operation
base
© Marcus Denker 17

MetaContext
metameta-
object
meta-2
link
level 1
meta-object
> Meta-level analysis:
meta
— Trace the tracer links
level 0
operation
base
© Marcus Denker 18

Future Work
> Generalize context model:
— Beyond the meta-context
> Virtual machine support
> Context-aware language kernel
© Marcus Denker 19

Conclusion
> Recursion problem
> Missing representation of meta-level execution
> Meta-context
— Solves the recursion problem
— Enables meta-level analysis
© Marcus Denker 20

Conclusion
> Recursion problem
> Missing representation of meta-level execution
> Meta-context
— Solves the recursion problem
— Enables meta-level analysis
Questions?
© Marcus Denker 21