问题
Let's have these classes:
class A {
fun foo(): A = this
}
class B: A() {
fun bar() { ... }
}
Now I would like Kotlin to detect when I call foo
on B
, and give me the result typed as B
. So that I can write:
B().foo().bar()
With kotlin 1.4.20, this is not possible - it would need an explicit cast to B
after foo()
.
Perhaps it could be handled by the compiler, if it clearly sees that the function returns this
. Or maybe we could hint it explicitly...
class A {
fun <Self> foo(): Self = this
}
I can't use extension function because I need the Java classes to have the properties.
I have read a this Kotlin forum thread on that topic, however I didn't see this case being solved. But maybe it's implied. Either way, it's not implemented at the moment.
One more nice article here.
I have read this SO question How to specify "own type" as return type in Kotlin and I have tried the "recursive type" approach, but it doesn't work if I want to have the type on the subclasses as well as base class:
Type parameter Me of 'HasStatus' has inconsistent values: BaseClass, Subclass
Is there any other trick to persuade Kotlin to return the type of this
if a method returns this
?
来源:https://stackoverflow.com/questions/65333206/kotlin-how-to-return-self-type-in-a-subclass-without-an-extension-function