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junior
Asked: 2020-08-06 07:40:15 +0800 CST 2020-08-06 07:40:15 +0800 CST

Can a higher order lambda function be created in kotlin?

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I'm reading the kotlin tutorial in codelads and this question came up, because in the codelabs they show us examples but not one of this type, so what I want is something like this:

var dirtyLevel = 20
val waterFilter: (Int) -> Int = { dirty -> dirty / 2}// funcion lambda
val updateDirty: Int = { dirty : Int, operation : (Int) -> Int -> operation(dirty)}// funcion lambda de orden superior
println(waterFilter(dirtyLevel))
println(updateDirty(30,waterFilter))

generates this error:

error: type mismatch: inferred type is (Int, (Int) -> Int) -> Int but Int was expected
val updateDirty: Int = { dirty : Int, operation : (Int) -> Int -> operation(dirty)}
                       ^

I also tried it like val updateDirty: Int = { (dirty : Int, operation : (Int) -> Int) -> operation(dirty)}this but it generates this error:

error: type mismatch: inferred type is (???) -> [ERROR : <ERROR FUNCTION RETURN TYPE>] but Int was expected
val updateDirty: Int = { (dirty : Int, operation : (Int) -> Int) -> operation(dirty)}
funciones

1 Answers

  1. Best Answer

    The syntax would be the following:

    val updateDirty: (Int, (Int) -> Int) -> Int = { num, operation -> operation(num) }
                  |A|  |-----B-----|    |C|     |D|  |----E--|    |-----F------|

    That is, we define a function called updateDirty, which accepts two parameters, the first of type integer (A), this is where we pass the 30, and the second parameter is a function that accepts an integer parameter and returns another integer ( B). This is where you pass waterFilter to it.

    Now for the implementation of the function, we indicate that it has two parameters: num (D), and y operation (E). And what the content of the function (F) does is call the function that we pass as a parameter in our case waterFilter, passing as a parameter the number that we pass to it, in our case 30.

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