Interface Declaration

An interface declares a set of method signatures that a type must satisfy. It lists method headers — names, parameters, and return types — but no bodies; the implementing type supplies those.

interface Display {
    func ToString() -> String;
}

interface Comparable {
    func CompareTo(other: self) -> int;
}

The keyword self stands for the implementing type, so Comparable above requires a CompareTo that takes another value of whatever type implements it. An interface may declare any number of methods.

See Also

• Interface Implementation — satisfying these signatures with extend
• Methods — how self works in a method