LYR-SEM0082

a member replacing a generic default of a generic interface

error · spec 05-interfaces

A conformer declares its own version of a generic method that a generic interface provides as a default.

Explanation

A generic method has no slot in a method table, and a default of a generic interface that calls it on this would reach the interface's version, not the conformer's. Until that is possible, a conformer may not stand in place of such a default.

Give the conformer's method another name.

Wrong

interface Source<T> {
    fn get(): T;
    fn pick<U>(u: U): U { return u; }
}

struct G :: [Source<int>] {
    n: int,
    fn get(): int { return this.n; }
    fn pick<U>(u: U): U { return u; }
}

fn main(): void {
    let _ = G { n = 1 }.get();
}

Right

interface Source<T> {
    fn get(): T;
    fn pick<U>(u: U): U { return u; }
}

struct G :: [Source<int>] {
    n: int,
    fn get(): int { return this.n; }
    fn choose<U>(u: U): U { return u; }
}

fn main(): void {
    let _ = G { n = 1 }.get();
}