Assume the following code:
class ConstructMe<T> {}
data class Test<T> constructor(var supplier: () -> ConstructMe<T>) {}
fun main(args: Array<String>) {
works<Int>()
breaks<Int>()
}
fun <T> works() {
Test<T>({ ConstructMe<T>() }) // (1) any one class type parameter can be removed like:
Test({ ConstructMe<T>() }) // (2) still works (class type inferred by argument type)
Test<T>({ ConstructMe() }) // (3) still works (argument type inferred by class type)
}
fun <T> breaks() {
Test<T>(::ConstructMe) // type interference failed (should probably work like (3); compiler improvement possible?)
Test<T>(::ConstructMe<T>) // type interference failed & type argument not allowed (language change necessary?)
}
I've run into this by passing JavaFX properties (SimpleIntegerProperty
, SimpleStringProperty
, ... and SimpleObjectProperty<T>
) to a generic class constructors () -> Property<T>
argument, where passing ::SimpleIntegerProperty
works without a problem, while ::SimpleObjectProperty
fails like the above example code.
Is it possible to improve the compiler here or to allow passing type parameters to constructor/function references? Does it even make sense to use constructor references over simple lambda expressions here? Does it compile any differently?
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