Passing lambda as an argument in Kotlin

Question

I'm using Kotlin and I'm trying to pass a lambda as a function parameter

var lambda = {existingEntity: SomeEntity?, param1: String? -> {
        val test = someFunction(existingEntity)
        existingEntity?.copy(name = param1)!!
     }}

    fun updateValue(param2: UUID, param1: String? = null): Mono<Boolean> {
        return updateFunc(param2, param1, lambda)
    }

    private fun updateFunc(param2: UUID, param1: String?, lambda: (SomeEntity?, String?) -> () -> SomeEntity): Mono<Boolean>{
        return repository.findById(param2)
            .flatMap {
                val existingEntity = it
                repository.update(existingEntity, lambda(it, param1))
                    .map { true }
            }
    }

Basically I want the lambda to return type SomeEntity. With the above implementation, the lambda returns () -> SomeEntity instead of SomeEntity. This causes an issue while calling repository.update().

How do I write the lambda to return SomeEntity instead of () -> SomeEntity ?

Answer 1

Whenever you wrap a fragment of code into {} you are getting a lambda. For example:

val v = "I am a value!" // String

val v = {
    "I am a function!"
} // () -> String

So...

val lambda: (SomeEntity?, String?) -> SomeEntity = { existingEntity: SomeEntity?, param1: String? ->
    val test = someFunction(existingEntity)
    existingEntity?.copy(name = param1)!!
}

As you can see what I did was removing the {} braces inside a lambda.