Rust中var和_var之间有什么区别？

Question

鉴于这种:

fn main() {
   let variable = [0; 15];
}

Rust编译器生成此警告:

= note: #[warn(unused_variables)] on by default
= note: to avoid this warning, consider using `_variable` instead

variable和之间有什么区别_variable？

Answer 1

区别在于前面的下划线,这导致Rust编译器允许它未被使用.它是裸下划线的命名版本,_可用于忽略值.

但是,_name行为不同于_.简单下划线会立即删除该值,同时_name像其他任何变量一样,并将值放在范围的末尾.

它的行为方式与普通下划线完全相同的示例:

struct Count(i32);

impl Drop for Count {
    fn drop(&mut self) {
        println!("dropping count {}", self.0);
    }
}

fn main() {
    {
        let _a = Count(3);
        let _ = Count(2);
        let _c = Count(1);
    }

    {
        let _a = Count(3);
        let _b = Count(2);
        let _c = Count(1);
    }
}

打印以下(游乐场):

dropping count 2
dropping count 1
dropping count 3
dropping count 1
dropping count 2
dropping count 3