How do I idiomatically call a nullable lambda in Kotlin?

Question

Given the following lambda:

val lambda: () -> Unit = null

Which of the following calls is idomatic to Kotlin for calling a nullable lambda?

lambda?.let { it() }

vs

lambda?.invoke()

This is gonna be up for personal opinions, but to give mine, the `let` usage here looks completely unnecessary, I always use just `?.invoke()`. — zsmb13, Aug 07 '18 at 19:08
If we're onto personal opinions, why not just make the lambda non-null and say `() -> Unit = {}`? — EpicPandaForce, Aug 07 '18 at 20:50

score 40 · Accepted Answer · answered Aug 07 '18 at 19:22

Let's ask Kotlin compiler:

 val lambda: (() -> Unit)? = null    
 lambda()

Compilers says:

Reference has a nullable type '(() -> Unit)?', use explicit '?.invoke()' to make a function-like call instead

So yeah, seems that ?.invoke() is the way to go.

Although even this seems fine by me (and by compiler too):

 if (lambda != null) {
      lambda()     
 }

score 2 · Answer 2 · answered Jul 28 '20 at 14:57

2

Here is a simple example:

fun takeThatFunction(nullableFun: (() -> Unit)?) {
    nullableFun?.let { it() }
}

takeThatFunction { print("yo!") }

answered Jul 28 '20 at 14:57

Yunus Emre

2 Answers2