Interface with generic type of the class implementing the interface?

Question

Having a class that implement a interface with generic type of "This" class

Is there a way to do this without a cast?

Simple code:

interface Triggerable<This: Triggerable<This>> { var trigger: (This) -> Unit fun triggerNow() = trigger(this as This) } class Test : Triggerable<Test>{ override var trigger: (Test) -> Unit = { /*...*/ } }

The same a little more complex:

interface TriggerInterface<T> { val trigger: (T) -> Unit fun triggerNow() } interface Triggerable<T: Triggerable<T>>: TriggerInterface<T> { override fun triggerNow() = trigger(this as T) } interface Signalable<T>: TriggerInterface<T> { var value: T override fun triggerNow() = trigger(value) } class Test : Triggerable<Test>{ override val trigger: (Test) -> Unit = { /*...*/ } }

EpicPandaForce · Accepted Answer · 2020-02-26 12:16:14Z

Should be possible like this

 interface TriggerInterface<T: TriggerInterface<T>> { val trigger: (T) -> Unit fun triggerNow() fun getThis(): T } interface Triggerable<T: TriggerInterface<T>>: TriggerInterface<T> { override fun triggerNow() = trigger(getThis()) } class Test : Triggerable<Test>{ override fun getThis(): Test = this override val trigger: (Test) -> Unit = { /*...*/ } }

Check http://www.angelikalanger.com/GenericsFAQ/FAQSections/ProgrammingIdioms.html#FAQ206

I would also personally recommend to reconsider if you really need both TriggerInterface AND Triggerable (where one inherits from the other).

It's needed because there is another interface which trigger another value
I accepted your answer because it's the best solution but not what I'm looking for. I ended using cast, because if the generic type argument "This" is well defined there will be no problem

Alex Krafts · Accepted Answer · 2020-02-26 07:59:41Z

Calling override fun triggerNow() = trigger(this as T) you are trying to cast Triggerable<T> to T thats why compiler warns you about unchecked cast

having

 val trigger: (TriggerInterface<T>) -> Unit

will allow you to call trigger with no casting

 override fun triggerNow() = trigger(this)

to actually execute

override val trigger: (Test) -> Unit = { /*...*/ }

you need an instance of Test to pass inside of trigger which is not declared anywhere in your code yet

Collectives™ on Stack Overflow

Interface with generic type of the class implementing the interface?

2 Answers 2

2 Comments

Comments

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Related