如何实现泛型枚举的“Serde::Deserialize”特性

让我们考虑以下示例通用枚举:

enum Enum<T, U> {
    T(T),
    U(U),
}

实施 Serde::Serialize 的特征 Enum 相当容易:

impl<T, U> Serialize for Enum<T, U>
where
    T: Serialize,
    U: Serialize,
{
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        match self {
            Enum::T(t) => t.serialize(serializer),
            Enum::U(u) => u.serialize(serializer),
        }
    }
}

然而,我很难实现 Serde::Deserialize 性状,其表现应如下:

• 如果值可以反序列化为类型 T ,那么它应该会返回 Enum::T(t) .
• 否则,如果值可以反序列化为类型 U ,那么它应该会返回 Enum::U(u) .
• 否则,它应该返回一个错误。

这是我能接近的:

impl<'de, T, U> Deserialize<'de> for Enum<T, U>
where
    T: Deserialize<'de>,
    U: Deserialize<'de>,
{
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        if let Ok(t) = T::deserialize(deserializer) {
            Ok(Enum::T(t))
        } else {
            if let Ok(u) = U::deserialize(deserializer) {
                Ok(Enum::U(u))
            } else {
                Err(D::Error::custom("Failed to deserialize Enum"))
            }
        }
    }
}

但是,我得到以下错误:

error[E0382]: use of moved value: `deserializer`
   --> src\lib.rs:731:47
    |
724 |         fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    |                           ------------ move occurs because `deserializer` has type `D`, which does not implement the `Copy` trait
...
728 |             if let Ok(t) = T::deserialize(deserializer) {
    |                                           ------------ value moved here
...
731 |                 if let Ok(f) = F::deserialize(deserializer) {
    |                                               ^^^^^^^^^^^^ value used here after move
    |
help: consider further restricting this bound
    |
726 |             D: Deserializer<'de> + std::marker::Copy,
    |                                  +++++++++++++++++++

For more information about this error, try `rustc --explain E0382`.

我知道发生了什么,但我不确定如何修复它(编译器的建议也不起作用)。