Typedefs

For Dart see here. For Kotlin see here

Kotlin

typealias IntList = List<Int>

typealias ListMapper<X> = Map<X, List<X>>

typealias Compare<T> = (a:T,b:T) -> Int

var il:IntList = listOf(1, 2, 3)
var m2:ListMapper<String>  = mapOf()

val sort:Compare<Int> = { a,b -> a-b }

// in Kotlin I cannot check the following,
// because kotlin generics has type erasure,
// in other words we cannot check if 
// sort is Compare<String> or Compare<Int>
// or any other type parameter  

 /* print(sort is Compare<String>); // false */

 print(sort is Compare<Int>) // true

Dart

typedef IntList = List<int>;

typedef ListMapper<X> = Map<X, List<X>>;

typedef Compare<T> = int Function(T a, T b);

int sort(int a, int b) => a - b;

IntList il = [1, 2, 3];
ListMapper<String> m2 = {};
print(sort is Compare<String>); // false

print(sort is Compare<int>); // true

Don't overuse typedef for function types

in Dart 1.0 if you wanted to use a function type for a field, variable, or generic type argument, you had to first define a typedef for it. From Dart 2.0 this is no more required