Single-expression functions

Until now, all our examples were declared in a normal way.

The function sum takes two Int values and adds them. Declared in a normal way, we must provide a body with curly braces and an explicit return:

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

Our sum function has its body declared inside curly braces with a return clause. But if our function is just one expression, it could have been written in a single line:

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

So, no curly braces, no return clause, and an equals (=) symbol. If you pay attention, it just looks similar to a lambda. 

If you want to cut even more characters, you can use type inference too:

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

Use type inference for a function's return when it is very evident which type you are trying to return. A good rule of thumb is to use it for simple...