How to pass functional interface operation as parameter in Kotlin?

Question

Given this functional interface in Java:

public interface Condition<T> {
   boolean check(T target);
}

The operation produce by that interface can be passed as parameter to the constructor of a class:

new ValidationRule<>(description,problem,target-> target.length() >= 2)

The third argument is a Condition interface where the operation to be perform is explicitly specified as:

target -> target.length() >= 2

I am having trouble duplicating this pattern in Kotlin. How can this be done in kotlin? Is there a kotlin specific way to do this.

PS I am new to Kotlin.

did you read chapters "lambdas" and "higher order functions" in the docs? — Tim
– Tim, Commented Aug 19, 2018 at 8:43
@TimCastelijns yes I did but I still have trouble understanding the this pattern and the pattern specified in that documentation can be used in similar ways! Maybe I just failed to understand — Eudy Contreras
– Eudy Contreras, Commented Aug 19, 2018 at 8:46
There are plenty of examples showing the syntax here: kotlinlang.org/docs/reference/lambdas.html. Have you at least tried anything? What? — JB Nizet
– JB Nizet, Commented Aug 19, 2018 at 9:18

EpicPandaForce · Accepted Answer · 2018-08-19 19:13:08Z

1

Should be as simple as

typealias Condition<T> = (T) -> Boolean

class ValidationRule<T>(val description: T, val problem: T, val condition: Condition<T>) 

val validationRule = ValidationRule(description, problem, { target -> target.length() >= 2 })

answered Aug 19, 2018 at 19:13

EpicPandaForce

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3 Comments

EpicPandaForce Over a year ago

If the interface already exists in Java, then you don't need the typealias.

Eudy Contreras Over a year ago

Thanks for the answer! The problem is not translating from one syntax to the other the problem is that the parameter wont accept the lambda expression as an argument.

EpicPandaForce Over a year ago

You might need to specify the , problem, Condition<SomeType> { target ->

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