Rust中的关联类型总结

trait Graph {
    type N;
    type E;

    fn has_edge(&self, n1: &Self::N, n2: &Self::N) -> bool;
    fn edges(&self, n: &Self::N) -> Vec<Self::E>;
}

trait A<T> {
    fn f(t: T) -> T;
}

struct S {}

// 第一个实现: A<String>
impl A<String> for S {
    fn f(t: String) -> String {
        t
    }
}

// 第二个实现：A<i32>
impl A<i32> for S {
    fn f(t: i32) -> i32 {
        t
    }
}

trait A {
    type Item;
    fn f(t: Self::Item) -> Self::Item;
}

struct S {}

impl A for S {
    type Item = i32;
    fn f(t: Self::Item) -> Self::Item {
        t
    }
}

trait Contains {
    type A;
    type B;

    fn contains(&self, _: &Self::A, _: &Self::B) -> bool;
}

// 不使用关联类型
fn difference<A, B, C>(container: &C) -> i32
where
    C: Contains<A, B>,
{
    ...
}

// 使用关联类型
fn difference<C: Contains>(container: &C) -> i32 {
    ...
}

struct Container(i32, i32);

trait Contains {
    type A;
    type B;

    fn contains(&self, _: &Self::A, _: &Self::B) -> bool;
    fn first(&self) -> i32;
    fn last(&self) -> i32;
}

impl Contains for Container {
    type A = i32;
    type B = i32;

    fn contains(&self, number_1: &i32, number_2: &i32) -> bool {
        (&self.0 == number_1) && (&self.1 == number_2)
    }

    fn first(&self) -> i32 {
        self.0
    }

    fn last(&self) -> i32 {
        self.1
    }
}

struct Container(i32, i32);

trait Contains {
    type A;
    type B;

    fn contains(&self, _: &Self::A, _: &Self::B) -> bool;
}

impl Contains for Container {
    type A = i32;
    type B = i32;

    fn contains(&self, number_1: &i32, number_2: &i32) -> bool {
        (&self.0 == number_1) && (&self.1 == number_2)
    }
}