Kotlin Functions And Lamdas

A function is a named block of code that performs a particular task. In Kotlin, a function always returns a value.

Declaring functions

Functions in Kotlin are declared as follows

fun (,,...):{ func body} </code>

Let us get a quick example of a function

fun sayHello()
{
    println("Hello from Kotlin")
}

The above function takes no parameters and returns type Unit.Unit is corresponds to void on the JVM.

Now a function that takes two parameters and returns a value demonstrated thus

fun welomeStudent(name:String,id:String):String{

    return "Welcome $name. Your student id is $id"

}

Calling functions

Functions in Kotlin are called the same way like most languages

<function name>(arg1,arg2,..argn)

Calling the above functions can be done as follows

sayHello()  //Prints Hello
welcomeStudent("Ngenge Senior","SC!1B373")

Now the beauty of Kotlin in functions come in when we can call functions using named parameters.

wecomeStudent(id="SX13A123","John Doe")

As you might have noticed, calling functions with named arguments, you can pass the arguments in any order. You might be asking how this helps us. Now imagine a function that you have just writtent that takes 20 parameters. Now, in a language like Java, you are compelled to know the order in which the parameters are passed to the function. But here with Kotlin, that order is not necessary.

Functions with Single expressions

We can write the function to add two integers as follows

fun add(a:Int,b:Int):Int{
    return a + b
}

The function has just a single expression. With Kotlin, we can simplify the function as follows

    fun add(a:Int,b:Int) = a+b

In this new version, we omit the return type as Kotlin will infer the type for us.

Functions with default values

Another awesome part of Kotlin is that it gives you the ability to give default values to your parameters. Let us take a real example. Say you are developing an app with two types of users, when user provides name, he/she is a regular user, but if not, they are anonymous

    fun greetUser(name:String = "Anonymous user",userId:Int = 0)
    {
        println("Welcome $name. Your user id is $userId")
    }

This function can be called in the following ways.

    greetUser() // prints Welcome Anonymous user. Your userid is 0
    ("Ngenge Senior")// Prints , Welcome Ngenge Senior. Your user id is 0
    greetUser(name="Romeo", userId=3) //Works as expected
    greetUser(userId=2,name="Julliet")