如何为本地特征实现 std::ops::Add？

Question

我有实现特征的对象：

trait X {
    fn transform_a(&self) -> Self;
    fn transform_b(&self) -> Self;
}

我想使用一些形式为 obj + Transform::A + Transform::B 的语法糖，所以我尝试了：

enum Transform {
    A, B
}

impl<T> std::ops::Add<Transform> for T where T: X {
    type Output = T;
    
    fn add(self, rhs: Transform) -> T {
        match rhs {
            Transform::A => self.transform_a(),
            Transform::B => self.transform_b(),
        }
    }
}

这行不通。我收到错误：

10 | impl<T> std::ops::Add<Transform> for T where T: X {
   |      ^ type parameter `T` must be covered by another type when it appears before the first local type (`Transform`)
   |
   = note: implementing a foreign trait is only possible if at least one of the types for which is it implemented is local, and no uncovered type parameters appear before that first local type
   = note: in this case, 'before' refers to the following order: `impl<..> ForeignTrait<T1, ..., Tn> for T0`, where `T0` is the first and `Tn` is the last

错误似乎说这是不可能的。如果可能，如何实现？

Playground

Answer 1

正如 E0210 上的文档向我指出的那样，不，这是不可能的。

如何为本地特征实现 std::ops::Add？

How to implement std::ops::Add for a local trait?

traits

rust