kotlin: syntax for 2 lambda parameter

Question

I'm new to kotlin. I have a java class with 2 overloaded methods. One accepts one function, the other one accepts two

mapToEntry(Function<? super T, ? extends V> valueMapper)

and

mapToEntry(Function<? super T, ? extends K> keyMapper, 
           Function<? super T, ? extends V> valueMapper)

nowm in kotlin, i'm trying to call the the version with 2 parameters (as in java):

myClass.mapToEntry(r -> r, r -> r)

but i get compilation error.

Kotlin: Unexpected tokens (use ';' to separate expressions on the same line)

what's the correct syntax?

hotkey · Accepted Answer · 2018-01-11 13:57:22Z

18

In Kotlin, lambda expressions are always surrounded by curly braces, so it's

myClass.mapToEntry({ r -> r }, { r -> r })

See: Lambda Expression Syntax

answered Jan 11, 2018 at 13:57

hotkey

149k43 gold badges392 silver badges333 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Todd · Accepted Answer · 2018-01-11 14:00:26Z

5

You were close, you just have to wrap them in curly braces...

myClass.mapToEntry({r -> r}, {r -> r})

Also, you can take advantage of the fact that Kotlin defines it as the default single parameter to a lambda. Assuming the key and value are both Strings, and you want to reverse the key and uppercase the value (just making up an example):

myClass.mapToEntry( { it.reversed() }, { it.toUpperCase() })

answered Jan 11, 2018 at 14:00

Todd

31.9k11 gold badges91 silver badges93 bronze badges

Comments

s1m0nw1 · Accepted Answer · 2018-01-11 18:33:14Z

4

Basic Syntax: Lambda expressions are always wrapped in curly braces:

val sum = { x: Int, y: Int -> x + y }

Example

Let's define a function similar to yours in Kotlin:

fun <T, K> mapToEntry(f1: (T) -> K, f2: (T) -> K) {}

The first possibily is straight forward, we simply pass two lambdas as follows:

mapToEntry<String, Int>({ it.length }, { it.length / 2 })

Additionally, it's good to know that if a lambda is the last argument passed to a function, it can be lifted out the parantheses like so:

mapToEntry<String, Int>({ it.length }) {
    it.length / 2
}

The first lambda is passed inside the parantheses, whereas the second isn't.

answered Jan 11, 2018 at 18:33

s1m0nw1

83k17 gold badges181 silver badges201 bronze badges

Collectives™ on Stack Overflow

kotlin: syntax for 2 lambda parameter

3 Answers 3

Comments

Comments

Example

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Example

Comments

Your Answer

Sign up or log in

Post as a guest

Related