Interfaces
Interfaces define a contract — a set of method signatures that a struct must provide. Any struct that provides an implementation of an interface via impl satisfies that contract and can be used wherever the interface type is expected.
Defining an Interface
An interface is declared with the interface keyword. The body contains method signatures — names, parameter types, and return types — but no implementations.
interface Drawable:
draw(self) -> str
interface Shape:
area(self) -> float
perimeter(self) -> float
The first parameter of every interface method must be self. It refers to the struct instance the method is called on.
Implementing an Interface
Use the impl keyword to provide a concrete implementation of an interface for a given struct. The block must define every method declared in the interface.
struct Circle:
radius: float
impl Shape for Circle:
fn area(self) -> float:
return 3.14159 * self.radius * self.radius
fn perimeter(self) -> float:
return 2.0 * 3.14159 * self.radius
struct Rectangle:
width: float
height: float
impl Shape for Rectangle:
fn area(self) -> float:
return self.width * self.height
fn perimeter(self) -> float:
return 2.0 * (self.width + self.height)Calling Interface Methods
Once a struct implements an interface, its methods are called using dot notation on an instance. The self parameter is passed automatically.
fn main():
let c: Circle = new Circle(5.0)
print(c.area()) # 78.53975
print(c.perimeter()) # 31.4159
let r: Rectangle = new Rectangle(4.0, 6.0)
print(r.area()) # 24.0