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In this blog, I’m going to explain higher-order functions.

A higher order function takes other function as a parameter or return a function as a result.

This is possible because functions are first-class value in scala. What does that mean?

It means that functions can be passed as arguments to other functions and functions can return other function.

The map function is a classic example of a higher order function.

Let’s define a function that doubles each value that is given to it.

will call List(1,2,3).map(x => doubleValue(x)) and gives us a list with values (1, 4, 9).  Function map will called on each element of the list that will be passed to doubleValue.

We can also give it an anonymous function.

map is a function which takes a function(x => x+1) and a list as its arguments and applies given function to all the elements of the list.

Let’s create our own higher order function:
Example 1:

addition takes higher order function as input which inturn takes two integers as input and returns an integer.

addition(squareSum, 1, 2) will call squareSum(1,2)
addition(cubeSum, 1, 2) will call cubeSum(1,2)
addition(intSum, 1, 2) will call intSum(1,2)

Example 2:

applyPatternToText functions takes another function as a parameter.

appendTag returns a function itself.

will call applyPatternToText(“scala”,appendTag(“scala”))

f:String => String will be replaced by appendTag(“scala”)

appendTag(“scala”) will print scala

Example 3:

Let’s take another example to find sum of a list and product of a list using higher order function:

operateList(List(1,2,3),(a, b) => a + b, “sum”) will call inner(List(1,2,3),0).

After match condition, next call will be inner(List(2,3),f(1,0)) which will give inner(List(2,3),1).

Next call would be inner(List(3),f(2,1)) which will give inner(List(3),3)
Next call would be inner(Nil,f(3,3)) which will give inner(Nil,6)

The final result would be 6.

Thanks for reading!

Written by 

Jyoti Sachdeva is a software consultant with more than 6 months of experience. She likes to keep up with the trending technologies. She is familiar with languages such as C,C++,Java,Scala and is currentky working on akka,akka http and scala. Her hobbies include watching tv series and movies, reading novels and dancing.

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