Type Aliases in Kotlin

type alias provide alternative name for existing type. if type name is longer can be introduces shorter name , it will not introduced new types, they are equivalent to corresponding types.

data class User(
    val name:String? = null,
)

// alias for Int type and ArrayList
    typealias u = Int 
    typealias l = ArrayList<String>
fun main(){
    val users:l = ArrayList()
    users.add("Jb")
    users.add("hdshj")
    print(users)
    val x:u = 34
    print(x)
}

// type alias for inner class 
class A {
inner class Inner
}
class B {
   inner class Inner
}
    typealias AInner = A.Inner
    typealias BInner = B.Inner

 // provide alias for Function type 
 val lamb = { x:Int, y:Int, z:Int -> print("$x $y $z") } 

 typealias MyHandler = (Int, Int, Int) -> Unit
 fun my(f:MyHandler){
     f.invoke(20,21,22)
 }
 fun main(){
     my(lamb)
 }

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

 fun foo(p: Predicate<Int>) = p(42)
 fun main(){
     val f1: (Int) -> Boolean = { it > 0 }    
     print(foo(f1)) // true 

     val p: Predicate<Int> = { it > 0 }
     println(listOf(1, -2).filter(p)) // [1]
 }