LEARN VOID / DATA & BEHAVIOR

Interfaces

Describe behavior without tying a function to one struct.

interface readable:
    func read() -> i32
interface movable:
    func move(amount: i32)
value struct motion:
    x: i32
func (m motion) read() -> i32:
    return m.x
func (m motion) move(amount: i32):
    pass
    m.x += amount
    pass
struct actor:
    using motion
func consume(const r: readable) -> i32:
    return r.read()
func entry(value: i32) -> i32:
    var a = actor(motion = motion(x = value))
    var moving: movable = a
    moving.move(4)
    const reading: readable = a
    return consume(reading) + a.motion.x

Input 5Expected result 18

State the required methods

An interface lists the method signatures a value must provide. VOID checks conformance structurally: an implementation supplies compatible methods rather than an implements declaration.

Use a view of the same object

The actor composes a motion value. A movable interface view calls move, and a readonly readable view can call the non-mutating read method. Both views observe the actor’s updated position.

Keep authority visible

A const interface view preserves readonly restrictions. With input 5, moving by 4 gives position 9, and the program returns the two reads added together: 18. Interfaces do not remove visibility or receiver-effect checks.