具有通用参数的Rust宏接受类型 [英] Rust macro accepting type with generic parameters

问题描述

我有一个实现特征impl_Trait!()的宏.现在，它适用于没有泛型参数的类型，但是我不确定如何将类型参数添加到impl关键字.

I have a macro that implements a trait, impl_Trait!(). Right now, it works for types without generic parameters, but I'm not sure how to add the type parameters to the impl keyword.

macro_rules! impl_FooTrait {
    ($name:ty) => {
        impl $crate::FooTrait for $name { ... }
    };
}

struct Bar(i32);
impl_FooTrait!(Bar);
// All OK

struct Baz<'a>(&'a i32);
impl_FooTrait!(Baz<'a>);
// use of undeclared lifetime name `'a`

推荐答案

您可以使用tt(单个令牌)标识符来接受您希望在另一个宏指令组中使用的生存时间(

You could use a tt (single token) identifier to accept a lifetime you want in another macro arm (playground link)

macro_rules! impl_FooTrait {
    ($name:ty, $lifetime:tt) => {
        impl<$lifetime> $crate::FooTrait for $name {  }
    };
    ($name:ty) => {
        impl $crate::FooTrait for $name {  }
    };
}

struct Bar(i32);
impl_FooTrait!(Bar);

struct Baz<'a>(&'a i32);
impl_FooTrait!(Baz<'a>, 'a); // Use and declare the lifetime during macro invocation

这是实际上实现某些内容的示例.

我猜这有点奇怪.我有兴趣查看其他替代答案.可能有更好的方法可以做到这一点.我还不熟悉宏观领域.

Its a bit weird to look at I guess. I am interested to see any alternative answers. There is possibly a nicer way to do this; I'm not well versed in macro land yet.

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