是否可以编写Rust宏"has_trait！(< type>，< ident> |< expr>))"? [英] Is it possible to write a Rust macro "has_trait!(<type>,<ident>|<expr>)"?

问题描述

我想比赛，例如一个实现特定特征的ident类型，我该怎么做?

I want to match, e.g. an ident's type to implement a certain trait, how would I do that?

这是(不完整的)代码中的基本概念:

Here the basic idea in (incomplete) code:

macro_rules! has_trait {
    ($ ($t : ty), ($x : ident),) => {

    } 
}

fn trait_test() {
    let a = vec![1, 2, 3];
    let b = 42;
    let a_iteratable = has_trait!(IntoIterator, a);
    let b_iteratable = has_trait!(IntoIterator, b);
    println!("{:?} iterable? {}", a, a_iteratable);
    println!("{:?} iterable? {}", b, b_iteratable);
}

我不能为如何说具有特征Foo的任何类型"而烦恼.

I cannot wrap my head around how to say "any type which has trait Foo".

我看到2种解决问题的方法:

I see 2 options how to tackle the problem:

1. 找到一个匹配表达式，该表达式匹配具有特征$t的任何类型，并在匹配时简单地返回true，否则(如何工作?)为false.
2. 在任何类型的匹配项的主体中，使用一些代码来确定特征$t是否由$x类型实现.

1. Find a match expression which matches any type with trait $t and simply return true on match, else (how works else?) false.
2. In the body of the match of any type, use some code to determine if trait $t is implemented by the type of $x.

我看不到如何做这两种选择.

I cannot see how to do either of both options.

这甚至可以做到吗?

推荐答案

您基本上想要的是静态(或编译时)反射: 根据类型系统，在编译时分配值以在运行时使用. 例如，在D甚至C ++中，这都是可能的，但在Rust中是不可能的.

What you basically want is static (or compile-time) reflection: Assigning values at compile-time, depending on the type system, to use at run-time. This is possible in for example D or even C++, but not in Rust.

Rust不允许模板专门化或编译时值作为通用参数，也没有像D这样的静态反射功能.

Rust does not allow template specialisation or compile-time values as generic parameters, nor does it have static reflection capabilities like D.

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