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]
}
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