相关疑难解决方法(0)

我有一个带字段的结构:

struct A {
    field: SomeType,
}

给定a &mut A,如何移动值field并交换新值？

fn foo(a: &mut A) {
    let mut my_local_var = a.field;
    a.field = SomeType::new();

    // ...
    // do things with my_local_var
    // some operations may modify the NEW field's value as well.
}

最终目标相当于一项get_and_set()行动.在这种情况下,我并不担心并发性.

我想收集结构的更改并立即应用它们.基本大纲如下所示:

enum SomeEnum {
    Foo,
    Bar,
}

struct SomeStruct {
    attrib: SomeEnum,
    next_attrib: Option<SomeEnum>,
}

impl SomeStruct {
    pub fn apply_changes(&mut self) {
        if let Some(se) = self.next_attrib {
            self.attrib = se;
        }
        self.next_attrib = None;
    }
}

这会产生以下编译器错误:

error[E0507]: cannot move out of borrowed content
  --> src/lib.rs:13:27
   |
13 |         if let Some(se) = self.next_attrib {
   |                     --    ^^^^ cannot move out of borrowed content
   |                     |
   |                     hint: to prevent move, use `ref se` or `ref mut se` …

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