Scala

# Scala Higher-Order Functions

When a function accepts another function as a parameter or returns another function as an output, it is referred to as a higher-order function. This refers to functions that interact with other functions. It is important to note that this higher-order function can be used with functions and methods that return the functions as results or take the functions as parameters. This is feasible because the Scala compiler permits the conversion of methods into functions. The idea of higher-order functions in Scala in Ubuntu 20.04 is explained in this article.

## Importance of Higher-Order Functions

Regarding the higher-order functions, some key points include:

• Higher-order functions are conceivable because the Scala programming language treats the functions as first-class values. This means that, like other values, the functions can be supplied as parameters or outputs, which is useful in providing a flexible way to write the programs.
• When constructing a function composition where functions may be created from other functions, it is advantageous. The method of composition known as “function composition” involves using two previously composed functions to create a single function.
• Lambda functions and anonymous functions can also be created with its help. The functions with no name but nevertheless function as functions are known as anonymous functions.
• It is applied to programs as well as cut down on the number of pointless lines of code.

## Example 1: Using a Function to Take Another Function as an Argument

Let’s consider the first example of a higher-order function. We pass the function in a given function as a parameter.

Here, the object is designated as “MyObject”. Then, within the object’s main definition, we called a function “func”. The function “func” takes the numeric value and the function “MultiplyByThree” as an input. We again invoked the function “func” to print the value of “x” which is passed as an input inside the “f”. Lastly, we set the operation “x*3” in the function “MultiplyByThree”.

As we passed the function “MultiplyByThree” inside the other function “func”, the function “func” outputs the result of the “MultiplyByThree” function as follows:

## Example 2: Using Anonymous Function as Lambda

An anonymous function does not have a name but performs the same function. When you don’t intend to repeat a function later, creating an anonymous version is a good idea. In Scala, the wild card operators “=>” rocket and “_” underscore can be used to generate anonymous functions.
Here is one to illustrate:

Within the main method of the object “MyDemo”, we created two variables. The variables are declared as “res1” and “res2”. The variable “res1” is initialized with the anonymous function by using the operator “=>”. The anonymous function is set with the x and y parameters and on the right side of the rocket “=>” operator we set the equation “x+y”. After that, we have another anonymous function which is employed with the wildcard “_”. Within the println method, we called the “res1” and “res2” respectively and assigned them two values.

The results for both the anonymous functions are generated as follows:

## Example 3: Using Multiline Expression

The term “multiline expression” refers to the expressions that span many lines. When utilizing the multiline expressions in Scala, use caution. To avoid issues regarding multiline expression, you can use the following methods:

The object “MyTest” has the definition of three functions. The first function is defined as “Sum1” which takes the parameters “i” and “j”. The input values “i” and “j” are set as “i+j” inside the function “Sum1” block. Next, we have another function as “Sum2” which also takes the input values and also set the operation “i+j”. After that, we defined the main method where two variables “Result1” and “Result2” are declared. These variables are called the functions “Sum1” and “Sum2” for passing the values against the “i” and “j”.

The output obtained by both functions “Sum1” and “Sum2” have the same results.

## Example 4: Using a Function Carrying

A method in Scala may have numerous parameter lists. A function that accepts the missing argument lists as arguments is produced when a function is called with fewer parameter lists than it requires. In other words, it is a method for changing a function that accepts several parameters into one that only accepts one.

Here, we created a function “Add” which takes two arguments separately. The “p” is the first argument and “q” is the second argument. Then, we declared a variable “result1” in the main method. The variable “Result1” is called the “Add” function and set the values for “p” and “q”. Also, we passed the single argument for the “Add” function which is called in the variable “AddValues”. The AddValues also takes the argument values of a number.

The results for the previous code upon compilation are as follows:

## Example 5: Using a Nested Function

Being a first-class function language, Scala enables you to pass the functions, return the functions, compose the functions, use the nested functions, and more. The definition and calling of nested functions are demonstrated in the following example:

Within the function “Sub1”, we defined another function “Sub2” which evaluates the difference between “a-b”. Outside the Sub2 function, we called the “Sub2” which takes the argument value “x” and the “Sub2(y, z)”. Next, we declared a variable “Result” which is called the Sub1 function and passed the numeric value to be evaluated for different operation.

The following is the different operation result generated by the previous code:

## Example 6: Using a Function with Variable Length Parameters

You can define the functions with parameters of variable length in Scala. Any quantity of arguments can be passed when calling the function.

To the function “add”, we set the variable “MySum” which is initially zero. Then, we have for loop which iterates over the numbers and increments by the MySum. Inside the main, we called the add function and passed the numerical values to it.

The length of the variable “MySum” is printed on the screen.

## Conclusion

We discovered from the aforementioned article that using the higher-order functions in Scala can make the code base simple and easy to comprehend for operations. Higher-order functions are those that accept or return the inputs from other functions. We also examined the examples demonstrating the various applications for these higher-order functions. Additionally, we learned how to hand over the anonymous functions as high-order functions.