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Sanjay Prajapat
Sanjay Prajapat

Posted on • Originally published at sanjayprajapat.hashnode.dev

Type Aliases in Kotlin

#kotlin #typealias #programming

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