Reflection: Stack as an Object Damien Cassou, Stphane Ducasse and - - PowerPoint PPT Presentation

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May 01, 2023 197 likes •350 views

Reflection: Stack as an Object Damien Cassou, Stphane Ducasse and Luc Fabresse W7S06 http://www.pharo.org Just to Reveal a Bit of It To let you know that it exists On demand the stack can be turned into an object We can walk but also

SLIDE 1

Reflection: Stack as an Object

Damien Cassou, Stéphane Ducasse and Luc Fabresse

W7S06

http://www.pharo.org

SLIDE 2

Just to Reveal a Bit of It

To let you know that it exists

On demand the stack can be turned into an object We can walk but also modify it W7S06 2 / 13

SLIDE 3

Coding in the Debugger

When a method is not found, we may end up with a

debugger

In the debugger, we can ask for the creation of a method

n the fly

The system compiles on the spot a special method Then it reexecutes the method It raises a shouldBeImplemented exception Then you can edit the method in the debugger Then proceed and the program continues to run W7S06 3 / 13

SLIDE 4

Operation Supporting Coding in the Debugger

On the fly method definition Stack navigation / manipulation W7S06 4 / 13

SLIDE 5

Stack Frame as an Object

Execution stack can be turned into a live object By default the stack is not an object

Can be reified on demand

Support exception definitions from within the language Basis for continuations and web serving W7S06 5 / 13

SLIDE 6

thisContext

thisContext is one of the three pseudovariables with self

and super

Returns an object that represents the method activation Can walk and change the stack Put self halt in the code to see it and walk W7S06 6 / 13

SLIDE 7

Example: Better Deprecated Message

We declare deprecation A >> foo self deprecated: 'Use bar.' on: '31/12/2015' in: 'Pharo50'. self bar should print: ’Message foo is deprecated in Pharo50. Use bar’

W7S06 7 / 13

SLIDE 8

Example: Better Deprecated Message

deprecated: anExplanationString on: date in: version "Warn that the sending method has been deprecated" (Deprecation method: thisContext sender method explanation: anExplanationString

n: date

in: version) signal

thisContext sender method returns compiled method A>>#foo

W7S06 8 / 13

SLIDE 9

Example: Conditional Halt and Test

How to halt a method that is heavily used? How to stop execution only from a given execution flow?

foo ... Halt if: #testSetInitialized ... Only halt if executed from testSetInitialized

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SLIDE 10

if: Implementation

Halt class >> if: condition "This is the typical message to use for inserting breakpoints during debugging. The argument can be one of the following:

− a block: if the Block has one arg, the calling object is bound

to that.

− an expression − a selector: Halt if found in the call chain"

condition isSymbol ifTrue: [ ^ self haltIfCallChainContains: condition ]. condition isBlock ifTrue: [ ^ self haltIfBlockWithCallingObject: condition]. condition ifTrue: [self signal].

W7S06 10 / 13

SLIDE 11

How if: is implemented?

Halt class >> haltIfCallChainContains: aSelector | cntxt | cntxt := thisContext. [ cntxt sender isNil ] whileFalse: [ cntxt := cntxt sender. (cntxt selector = aSelector) ifTrue: [ self signal ] ].

W7S06 11 / 13

SLIDE 12

Foundation for Innovation

Continuations Seaside: Powerful dynamic web framework for dynamic

web applications

http://www.seaside.st
http://book.seaside.st

W7S06 12 / 13

SLIDE 13

A course by and in collaboration with

Inria 2016 Except where otherwise noted, this work is licensed under CC BY-NC-ND 3.0 France https://creativecommons.org/licenses/by-nc-nd/3.0/fr/