types - 创建一个基本上是 String 但与 String 不兼容的类型？

Question

我注意到在我的项目中，我使用了很多 String 类型，我并不是真正的 String 类型，而是 String 中包含的特定类型的值code>String，无法区分，例如通过使用正则表达式，但应该从代码的角度加以区分。有没有办法让编译器帮助我？例如，考虑这个函数:

fn do_something(val1: String, val2: String) {}

fn main() {
    let val1: String = "hello";
    let val2: String = "hello2";
    do_something(val1, val2);
}

有没有一种方法可以创建 SpecificStringType1 和 SpecificStringType2，以便第一个 do_something 调用可以编译，但第二个不能？

fn do_something(val1: SpecificStringType1, val2: SpecificStringType2) {}

fn main() {
    let val1: SpecificStringType1 = "hello";
    let val2: SpecificStringType2 = "hello2";
    let val3: SpecificStringType2 = "hello2";
    let val4: SpecificStringType2 = "hello2";
    do_something(val1, val2);
    do_something(val3, val4);
}

Answer 1

你可以用元组结构包裹 String，创建一个新的不同类型:

// This is a custom type which just wraps String,
// however you can choose what it derives again.
#[derive(Clone, Debug)]
struct MyString(String);

// Since they are distinct types, type check will prevent using
// String as MyString and vice versa.
fn f1(s: &String, t: &String) -> bool {
    return true;    
}

fn f2(s: &String, t: &MyString) -> bool {
    return false;
}

fn main() {
    let s: String = "hello".to_string();
    let ms = MyString("goodbye".to_string());
    let MyString(ms_inner) = ms.clone();

    println!("{:?}", &s);
    println!("{:?}", &ms);

    // Here is proof that it works.
    println!("{}", f1(&s, &ms_inner));
    println!("{}", f2(&s, &ms));
}

https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=a32994fab2cabb6495807726f246da1e