Rust 如何连接字符串

连接字符串时，需要分配内存来存储结果.最简单的开始是String和&str:

fn main() {
    let mut owned_string: String = "hello ".to_owned();
    let borrowed_string: &str = "world";
    
    owned_string.push_str(borrowed_string);
    println!("{}", owned_string);
}

在这里，我们拥有一个可以变异的字符串.这是有效的，因为它可能允许我们重用内存分配.String和String也有类似的情况，比如&Stringcan be dereferenced as &str.

fn main() {
    let mut owned_string: String = "hello ".to_owned();
    let another_owned_string: String = "world".to_owned();
    
    owned_string.push_str(&another_owned_string);
    println!("{}", owned_string);
}

在此之后，another_owned_string保持不变(注意mut限定符).还有另一个变体consumes和String相同，但不要求它是可变的.这是一个implementation of the Add trait，以String为左侧，&str为右侧:

fn main() {
    let owned_string: String = "hello ".to_owned();
    let borrowed_string: &str = "world";
    
    let new_owned_string = owned_string + borrowed_string;
    println!("{}", new_owned_string);
}

请注意，拨打+后，owned_string将不再可用.

如果我们想制作一个新的字符串，让两者都保持不变呢？最简单的方法是使用format!:

fn main() {
    let borrowed_string: &str = "hello ";
    let another_borrowed_string: &str = "world";
    
    let together = format!("{}{}", borrowed_string, another_borrowed_string);

    // After https://rust-lang.github.io/rfcs/2795-format-args-implicit-identifiers.html
    // let together = format!("{borrowed_string}{another_borrowed_string}");

    println!("{}", together);
}

请注意，这两个输入变量都是不可变的，因此我们知道它们不会被触碰.如果我们想对String的任意组合做同样的事情，我们可以利用String也可以格式化的事实:

fn main() {
    let owned_string: String = "hello ".to_owned();
    let another_owned_string: String = "world".to_owned();
    
    let together = format!("{}{}", owned_string, another_owned_string);

    // After https://rust-lang.github.io/rfcs/2795-format-args-implicit-identifiers.html
    // let together = format!("{owned_string}{another_owned_string}");
    println!("{}", together);
}

不过你不需要用format!.您可以 Select clone one string并将另一个字符串附加到新字符串:

fn main() {
    let owned_string: String = "hello ".to_owned();
    let borrowed_string: &str = "world";
    
    let together = owned_string.clone() + borrowed_string;
    println!("{}", together);
}

Note-我所做的所有类型规范都是多余的-编译器可以推断出这里使用的所有类型.我添加这些问题只是为了让新Rust 的人明白，因为我希望这个问题会受到该群体的欢迎！