An implementation of slot with type-checking.

In a playground, execute the following script:

Metacello new
	repository: 'github://juliendelplanque/TypedSlot/src';
	baseline: 'TypedSlot';
	load

This project provides 4 kinds of "type" to provide to TypedSlot:

• Class: The slot will only accept objects that are kind of a given class.
• Trait: The slot will only accept objects for which the class is using a given trait.
• Block: The slot will only accept objects for satisfying a given block (i.e. the block returns true).
• Interface: The slot will only accept object for which the class implement a given interface.

It is possible to enable/disable type checking on multiple level:

• Globally, a setting is available in the "Tools" section of the settings.
• At class-level by overriding class-side method #isTypeCheckingEnabled to let it return true (returns false by default).
• At instance-level by overriding instance-side method #isTypeCheckingEnabled to define a custom policy at instance level (using an instance variable for example).

One can define an object with a slot that can only accept integers.

Object subclass: #ExampleTypedSlotUsingClass
	slots: { #integerSlot type: Integer }
	classVariables: {  }
	package: 'TypedSlot-Example'

Once this class is defined and the accessor and mutator for #integerSlot are defined, one can expect the following behaviour.

object := ExampleTypedSlotUsingClass new.

object integerSlot. "nil"
object integerSlot: 1.
object integerSlot. "1"

object integerSlot: 'str'. "Raises a TypeViolation exception."

One can define an object with a slot that can only accept objects for which the class uses a given trait.

Object subclass: #ExampleTypedSlotUsingTrait
	slots: { #assertableSlot type: TAssertable }
	classVariables: {  }
	package: 'TypedSlot-Example'

Once this class is defined and the accessor and mutator for #assertableSlot are defined, one will only be able to set assertable objects in the #assertableSlot.

One can define an object with a slot that can only accept integers.

Object subclass: #ExampleTypedSlotUsingBlock
	slots: { #greaterThanZeroSlot type: [ :x | x > 0 ] }
	classVariables: {  }
	package: 'TypedSlot-Example'

Once this class is defined and the accessor and mutator for #greaterThanZeroSlot are defined, one can expect the following behaviour.

object := ExampleTypedSlotUsingBlock new.

object greaterThanZeroSlot. "nil"
object greaterThanZeroSlot: 1.
object integerSlot. "1"

object greaterThanZeroSlot: -1. "Raises a TypeViolation exception."
object greaterThanZeroSlot: 'test'. "Raises a TypeViolation exception because it does not understand some message."

To be documented once this feature is stable. In the meantime, take a look at TypedSlotInterfaceTest and TypedSlotRemoteInterfaceTest.