Understanding Infix Functions in Kotlin

Kotlin, one of the most popular languages for Android development, is loaded with a plethora of features designed to ease the life of developers. One such feature that can significantly improve code readability and user-friendly interfaces is the Kotlin infix function. Today, we delve into the world of Kotlin infix functions to explain what they are, and how to use them.

What is an infix function in Kotlin?

An infix function in Kotlin is a type of function that can be called using infix notation, which means you can call the function without using parentheses () and dot ..

Here is a simple structure of the infix function:

fun ClassName.functionName(param: ParamType): ReturnType {...}

To mark a function as an infix function, we use the infix keyword. So, the structure becomes:

infix fun ClassName.functionName(param: ParamType): ReturnType {...}

Example of an infix function:

Let's say you have a class called Person and you want to define a function that checks if the person is of a certain age. Here's how you would define and use an infix function for this purpose:

class Person(var age: Int) {

    infix fun isOfAge(requiredAge: Int): Boolean {
        return this.age >= requiredAge
    }
}

fun main() {
    val john = Person(22)

    // Using infix notation
    if (john isOfAge 18) {
        println("John is of age.")
    } else {
        println("John is not of age.")
    }
}

In the above example, isOfAge is an infix function. We can call it using the infix notation john isOfAge 18, which is easier to read compared to the normal function call notation john.isOfAge(18).

Where can we use infix functions?

Infix functions enhance the readability of your code, making it more fluent and closer to plain English. They are particularly handy when defining operators or creating your custom domain-specific language (DSL) with a specific syntax. Infix functions can also be used with extension functions to extend the functionality of existing classes.

However, to be eligible to be marked as an infix function, the function must be a member function or an extension function, it must have a single parameter, and the parameter must not accept a variable number of arguments and must have no default value.

Conclusion

Kotlin infix functions are a powerful tool that can dramatically improve the readability of your code and facilitate the creation of more fluent APIs and Domain-Specific Languages (DSLs). However, like any tool, they should be used judiciously and wisely. It is always paramount to keep in mind the specific requirements of your project and the readability of your code. With infix functions in your Kotlin toolkit, you can confidently create cleaner, more readable code. Happy coding!