Question

如何在嵌套结构的实例中更改字段的值？

// Do Not Change - Start

struct Base {
    val: String,
}

struct Level1 {
    val: Base,
}

struct Level2 {
    val: Level1,
}

// Do Not Change - End

fn main() {
    let x = Level2 {
        val: Level1 {
            val: Base {
                val: "World".to_string(),
            },
        },
    };

    println!(" Hello {}", x.val.val.val);

    x.val.val.val = "Moon".to_string();

    println!(" Hello {}", x.val.val.val);
}

playground

error[E0594]: cannot assign to field `x.val.val.val` of immutable binding
  --> src/main.rs:28:5
   |
18 |     let x = Level2 {
   |         - help: make this binding mutable: `mut x`
...
28 |     x.val.val.val = "Moon".to_string();
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot mutably borrow field of immutable binding

Answer 1

我强烈建议您返回并重新阅读The Rust Programming Language，尤其是有关variables and mutability的章节。

按照编译器的提示执行操作：

<?php
?>

<script>
var spans = document.getElementsByTagName("span");

for (var i=0; i < spans.length; i++)
{
    if (spans[i].innerHTML.contains("Archives"))
    {
        //is this the "Welcome" span?
        spans[i].innerHTML = "test string";  //change to new value
        break;                               //hop out of the loop, we're done
    }
}
</script>

 help: make this binding mutable: `mut x`

另请参阅：

无法可变地借用不可变绑定的字段

1 个答案: