peteruhnak/assign-reifs.png

title: MetaLinks notes tags: [Pharo, MetaLinks, Reflectivity] category: Pharo

Available reifications

"Available reifications"
RBProgram>>availableReifications

Many reifications are available for all nodes, namely

RFReification allSubclasses select: [ :each |
	each entities includes: RBProgramNode
] thenCollect: #key

" == common reifications ==
#object
#link
#node
#context
#class
#entity"

For AssignmentNode, the reifications newValue and value will be the same if you use control: #after. They will be (correctly) different only for control: before.

Maybe oldValue could be introduced for #after in the future.

Reifications as arguments to conditions.

When the block used as a condition has arguments, the name is matched to the possible reifications and if valid this value is passed as an argument. Very useful e.g. for object specific links:

link := MetaLink new
	condition: [ :object | object == <the object I am intersted in> ];
	metaObject: <someObject>;
	selector: <some selector>

Reifications as meta object

Every valid reified value can be the metaobject of the link. e.g. you can now define a link where the meta is the node where the Link is installed:

link := MetaLink new
	metaObject: #node;
	selector: #tagHasBeenExecuted.

Or the #receiver:

link := MetaLink new
	metaObject: #receiver;
	selector: #perform:withArguments:;
	arguments: #(selector arguments).

One-time use MetaLinks (`optionOneShot`)

X) optionOneShot (options:, optionOneShot: true)

link := MetaLink new
                metaObject: self;
                options: #(optionOneShot);
				optionOneShot: true;
                selector: #tagExec.

The full test looks like this:

testLinkOneShot
	| sendNode link |
	sendNode := (ReflectivityExamples>>#exampleMethod) sendNodes first.
	link := MetaLink new
		metaObject: self;
		options: #(optionOneShot);
		selector: #tagExec.
	sendNode link: link.
	self assert: sendNode hasMetalink.
	self assert: tag isNil.
	self assert: (ReflectivityExamples new exampleMethod = 5).
	self assert: (tag = #yes).
	self deny: sendNode hasMetalink.
	tag := nil.
	self assert: (ReflectivityExamples new exampleMethod = 5).
	self assert: tag isNil.

Disabl

Options for metalinks

The latest image now has some more options for meta links. The complete list is listed in the #defaultOptions method of MetaLink class:

defaultOptions
	^ #(
	+ optionInlineMetaObject            "meta object is inlined by default."
	+ optionInlineCondtion              "condition is inlined by default.”  (ups, typo, will fix)
	- optionCompileOnLinkInstallation   "generate compiledMethod on link installation"
	- optionOneShot                     "remove link after first activation"
	- optionMetalevel                   "force level: 0 for the link"
	- optionDisabledLink                "links are active by default"
	)

Some of the options make only sense because after this issue will be integrated:

https://pharo.fogbugz.com/f/cases/16695/allow-classes-to-force-meta-link-options-metaLinkOptions

we will have a mechanism that classes can enforce options for all links installed in them. This is done by adding a method on the instance or class side like this:

metaLinkOptions
	^{
	#exampleMethodWithMetaLinkOptionsViaClass -> #( + optionCompileOnLinkInstallation)
	}

This allows e.g. a class to turn off links for one method or enforce using meta-level awareness. (for now the options are overridden when installing a link, I will move this into the code generator to have a real overlay semantics as a next step).