static - 静态特征函数的 Rust 类型提示

Question

考虑这个例子:

trait MyTrait {
    fn maybe_new() -> Option<Self>;
}

impl MyTrait for i32 {...}

fn hello() {
    match MyTrait::maybe_new() {
        Some(x) => ...,
        None => ...,
    }
}

编译失败，因为无法推断 x 的类型。有没有什么方法可以添加一个类型注解来完成这项工作，而不必将 maybe_new() 分解成这样的 let 语句？:

let p:Option<i32> = MyTrait::maybe_new();
match p {
    Some(x) => ...,
    None => ...,
}

Answer 1

参见 How do I provide type annotations inline when calling a non-generic function? .在您的情况下，它看起来像这样:

match <i32 as MyTrait>::maybe_new() {
    Some(x) => ...,
    None => ...,
}