Higher order functions

`Definition`

Higher-order functions are the ones that take functions as parameters or return function as a result.
We can even store the higher-order function in a variable and a data structure.
They enable functional programming concepts and allow you to write more concise and expressive code.

Functions in kotlin have a type
The same way as we can declare Int,String,Person we can declare something of type function
A type is composed of FunctionParameters + FunctionReturnType
(Parameters are declared within these brackets) --> ReturnType

A function that takes a single parameter Int and returns a Unit(A unit means nothing like void)

(Int) -> Unit

A function that takes two parameters Int and String and returns Unit

(Int,String) -> Unit

A function that takes String as a parameter and returns Int

(String) -> Int

We can pass functions to other functions and return functions from others.
How we do this
- Declare a function as having another function as a parameter.
- When using the first function, We pass the second function as an argument.

kotlin