What's the meaning of plus sign before a Kotlin method?

问题

I'm studiyng Kotlin and was watching the AndroidDevSummit, more specifically the presentation "Undestanding Compose" from Leland Richardson.

While the presentation (at 28min26sec), he shown the following code:

@Composable
fun App(items: List<String>, query: String) {
    val results = +memo(items, query) {
        items.filter { it.matches(query) }
    }
    // ...
}

What does the "+" plus sign before the "memo" method?

回答1:

+ is kind of like an operator invoke for effects. The functions that return effects just return an object for the effect and the + says, "add it into the composition here"

by Adam Powell on Kotlin Slack

The full thread on kotlin slack

The + operator will be removed in the future, for states, probably will use Property Delegates, something like this: var myState by state { "value" }

来源：https://stackoverflow.com/questions/58571670/whats-the-meaning-of-plus-sign-before-a-kotlin-method