Map with function

Support
1

Hi,
I tried a list with function (ki-shell 1.7.0) :

[48] val square = fun(x:Int) : Int {return x*x}
[49] val cube = fun(x:Int) : Int {return x*x*x}
[50] val l_power=mutableListOf(square, cube)
[51] l_power[0](5)
res27: Int = 25

Now with a map

[52] val m_power=mutableMapOf("power2" to square, "power3" to cube)
type results for list or map seems equal

[53] m_power["power2"]
res29: Function1<Int, Int> = (kotlin.Int) -> kotlin.Int
[54] l_power[0]
res30: Function1<Int, Int> = (kotlin.Int) -> kotlin.Int

Now if I call function there is an error :

[55] m_power["power2"](5)
ERROR Reference has a nullable type '((Int) -> Int)?', use explicit '?.invoke()' to make a function-like call instead (Line_56.kts:1:1)

Where is my mistake?

2

The get operator on map returns a nullable type, since it doesn’t know if the key exists in the map at all.

You can use getValue - Kotlin Programming Language instead which will return a non-nullable type, but throw if the value isn’t there.

2 Likes
3

thanks it works :

m_power.getValue("power2")(5)

res34: Int = 25
4

But still, why does the shell print the wrong type for m_power[“power2”]? It should be a nullable type, but in the output in the OP it’s a non-nullable type.

5

The shell prints the type of the actual returned value (which is not null in your case), not the return type of the invoked function.

2 Likes
6

Why should it be nullable? It’s type of the value it got and it got value previously assigned to square

1 Like
7

Right, thanks — I missed that it was printing the result type, not the expression type.