Android Development with Kotlin

What is function type under the hood?

Under the hood, function types are just a syntactic sugar for generic interfaces. Let's look at some examples:

• The ()->Unit signature is an interface for Function0<Unit>. The expression is Function0, because it has zero parameters, and Unit because it is the return type.
• The (Int)->Unit signature is interface for Function1<Int, Unit>. The expression is Function1 because it has one parameter.
• The ()->(Int, Int)->String signature is an interface for Function0<Function2<Int, Int, String>>.

All of these interfaces have only one method, invoke, which is an operator. It allows an object to be used like a function:

    val a: (Int) -> Unit = //... 
    a(10)        // 1 
    a.invoke(10) // 1 

1. These two statements have the same ...