Extension Functions

Extension Functions

Extension functions are functions that may be invoked on an object, like it was an entity that has the function defined in it. They may be applied to any type, using the on keyword in the following format:

fun printThis(str) on string {
    printf("Printing this string: ''%s;", [str])
}

"My String".printThis()  // Prints "Printing this string: 'My String'"

The first parameter of the function definition is the object that the function is bring invoked on. Notice that it is implicitly set, and is not included in the call to the function. Other parameters may be added after that, such as the following:

fun printThis(str, n) on string {
    for (i..n) {
        printf("Printing this string: ''%s;", [str])
    }
}

"My String".printThis(2)  // Prints "Printing this string: 'My String'" twice

Extension functions also work for entities.

entity Cat {
    string name

    Cat(name)
}

fun sayHi(cat) on Cat {
    printf("Hello, %s", [cat.name])
}

Cat cat = new Dat("Olive")
cat.sayHi()  // Prints "Hello, Olive"

Native Method Extensions

Extension methods may be native methods too. The only difference in definition is they don't include the invoked on parameter, and as normal for native functions, don't include a body.

native fun sayHi() on Cat

For implementing these, see Native Methods.