BuilderInference

Allows to infer generic type arguments of a function from the calls in the annotated function parameter of that function.

When this annotation is placed on a generic function parameter of a function, it enables to infer the type arguments of that generic function from the lambda body passed to that parameter.

The calls that affect inference are either members of the receiver type of an annotated function parameter or extensions for that type. The extensions must be themselves annotated with @BuilderInference.

Example: we declare

fun <T> sequence(@BuilderInference block: suspend SequenceScope<T>.() -> Unit): Sequence<T>

and use it like

val result = sequence { yield("result") }

Here the type argument of the resulting sequence is inferred to String from the argument of the SequenceScope.yield function, that is called inside the lambda passed to sequence.

Note: this annotation is experimental, see ExperimentalTypeInference on how to opt-in for it.