Rust by Example

12.2 Implementation

Similar to functions, implementations require care to remain generic.

struct S; // Concrete type `S`
struct GenericVal<T>(T,); // Generic type `GenericVal`

// impl of GenericVal where we explicitly specify type parameters:
impl GenericVal<f32> {} // Specify `f32`
impl GenericVal<S> {} // Specify `S` as defined above

// `<T>` Must precede the type to remain generic
impl <T> GenericVal<T> {}
struct Val {
    val: f64
}

struct GenVal<T>{
    gen_val: T
}

// impl of Val
impl Val {
    fn value(&self) -> &f64 { &self.val }
}

// impl of GenVal for a generic type `T`
impl <T> GenVal<T> {
    fn value(&self) -> &T { &self.gen_val }
}

fn main() {
    let x = Val { val: 3.0 };
    let y = GenVal { gen_val: 3i32 };

    println!("{}, {}", x.value(), y.value());
}

See also:

functions returning references, impl, and struct