Higher order functions in Swift: Filter, Map, Reduce, flatmap, compactMap

Ever since I learned about functions and closures in detail, I wanted to know more about the advantages and usages of these in programming. I read about higher order functions that can be used on collection types and this is what I understood.

I don’t know who that is over there at the top.

As far as I understood, higher order functions are functions that takes another function/closure as argument and returns it.

I will try to explain this first. Consider the following code which will give you an idea what a higher order function is :

Pass function to another function:

higher order functions in swift

The first two methods are of type (Double,Double)->Double . First one accepts two double values and return their sum . The second one returns the product of these two double values. The third method is a higher order function which accepts three parameters. Two double values and a function of type (Double,Double)->Double . Do have a look at the method call. You will understand how a higher order function works.

Return function from another function:

Here , the function doArithmeticOperation(isMultiply:) is a higher order function which returns a function of type (Double,Double)->Double .

Functions and closures are first class members in swift. They can be saved into a variable and passed around.

So, here , based on the bool value passed into the doArithmeticOperation(isMultiply:) function, it returns the function which does the operation.

operationToPerform_1 is a function that does the multiplication for you.

operationToPerform_2 is a function that does the addition for you.