有没有一种方法可以在循环的条件表达式中分配变量？

Question

Rust中的C表达式是否等效？

int x;
while ((x = get_num()) < 5) {
    printf("x is %d, but less than 5\n", x);
}

get_num()是一个接受用户输入并返回整数的函数。

到目前为止，我能想到的最好的方法是：

while let Some(x) = {let y = get_num(); if y < 5 {Some(y)} else {None}}  {
    println!("x is {}, but less than 5", x);
}

Answer 1

从Rust 1.28开始，您可以使用iter::repeat_with：

for x in iter::repeat_with(get_num).take_while (|x| *x < 5) {
    println!("x is {}, but less than 5", x);
}

但无聊可能更好：

loop {
    let x = get_num();

    if x >= 5 {
        break;
    }

    println!("x is {}, but less than 5", x);
}

Eventually, there might在语法上应等效。

// doesn’t exist yet!
while let x = get_num() && x < 5 {
    println!("x is {}, but less than 5", x);
}