Functions

Kotlin has a very powerful support for functional programming. Having that in mind, it is important to know functions really well 😉 and I guess that's why you're here.

Basic

How do I write a kotlin function?

fun hello(){
    println("Hello!")
}

info

• we use the fun keyword to declare a function, isn't it funny and fun 🕺 💃
• this is followed by the function name which in this case is hello
• adding parenthesis () that will contian our parameters
• finally adding braces {} for our function body

But what about using it?

hello()

> Hello!

Another thing, you've mention parameters in the info section there, what are they?

Parameters

Parameters are placeholders declared in a function, they don't have concrete values

Arguments on the other hand are now the actual values passed to a function when it is being used

Umm okay 🤨 do you have an example?

fun markAsRead(book: String){ // book here is a PARAMETER
    println("Hello $book!")
}

markAsRead("Kotlin") // "Kotlin" is an ARGUMENT
> Hello Kotlin!

info

• book is declared as a parameter (placeholder)
• "Kotlin" is the argument for the book parameter
• parameters are declared by specifiying the name of the parameter followed by the type
• you can declare more than one parameter for any function, just specify the name and type followed by a comma

What if I want to add more than one parameter?

fun hello(greeting: String, name: String){
    println("$greeting $name!")
}

hello("Jambo", "Kotlin")
> Jambo Kotlin!

Usecases

Functions are used everywhere in the kotlin language, an example is creating any list

fun main(){
    val list = listOf(1,2,3)
    println(list)
}

> [1,2,3]

In the example above, listOf and println are examples of Kotlin functions found in the standard library.

There's so much more you can learn about functions like named arguments and default values just to mention a few.