Question

代码是让score_handler在方法operation（）中处理某所学校的分数，handle（）只是进行一些计算而不是保留self.school的引用：

trait Class{
    fn student_count(&self, )->usize;
    fn student_score(&self, i: usize) ->u64;
}

trait School<'a>{
    fn class_count(&self)->usize;
    fn class(&'a self, i:usize)->&'a dyn Class;
}

trait ScoreHandler<'a> {
    fn handle(&'a mut self, school: &'a dyn School<'a>);
}

struct Coordinator<'a>{
    some_value: u64,
    school: &'a dyn School<'a>,
    score_handler: &'a mut dyn ScoreHandler<'a>
}

impl Coordinator<'_>{
    pub fn main(&mut self){
        self.operate();
        if self.some_value == 0 {
            println!("0");
        }
    }
    fn operate(&mut self){
        self.score_handler.handle(self.school);
    }
}

我遇到了错误：

error[E0495]: cannot infer an appropriate lifetime for autoref due to conflicting requirements
  -> mytest/main/src/main.rs:29:28
   |
29 |         self.score_handler.handle(self.school);
   |                            ^^^^^^
   |
note: first, the lifetime cannot outlive the anonymous lifetime #1 defined on the method body at 28:5...
  -> mytest/main/src/main.rs:28:5
   |
28 | /     fn operate(&mut self){
29 | |         self.score_handler.handle(self.school);
30 | |     }
   | |_____^
note: ...so that reference does not outlive borrowed content
  -> mytest/main/src/main.rs:29:9
   |
29 |         self.score_handler.handle(self.school);
   |         ^^^^^^^^^^^^^^^^^^
note: but, the lifetime must be valid for the lifetime `'_` as defined on the impl at 21:18...
  --> mytest/main/src/main.rs:21:18
   |
21 | impl Coordinator<'_>{
   |                  ^^
note: ...so that the types are compatible
  --> mytest/main/src/main.rs:29:28
   |
29 |         self.score_handler.handle(self.school);
   |                            ^^^^^^
   = note: expected `&mut dyn ScoreHandler<'_>`
              found `&mut dyn ScoreHandler<'_>`

...

因此我将<'_>更改为<'a>，如下所示：

trait Class{
    fn student_count(&self, )->usize;
    fn student_score(&self, i: usize) ->u64;
}

trait School<'a>{
    fn class_count(&self)->usize;
    fn class(&'a self, i:usize)->&'a dyn Class;
}

trait ScoreHandler<'a> {
    fn handle(&'a mut self, school: &'a dyn School<'a>);
}

struct Coordinator<'a>{
    some_value: u64,
    school: &'a dyn School<'a>,
    score_handler: &'a mut dyn ScoreHandler<'a>
}

impl<'a> Coordinator<'a>{
    pub fn main(&'a mut self){
        self.operate();
        if self.some_value == 0 {
            println!("0");
        }
    }
    fn operate(&'a mut self){
        self.score_handler.handle(self.school);
    }
}

我得到了错误：

error[E0503]: cannot use `self.some_value` because it was mutably borrowed
  --> mytest/main/src/main.rs:24:12
   |
21 | impl<'a> Coordinator<'a>{
   |      -- lifetime `'a` defined here
22 |     pub fn main(&'a mut self){
23 |         self.operate();
   |         --------------
   |         |
   |         borrow of `*self` occurs here
   |         argument requires that `*self` is borrowed for `'a`
24 |         if self.some_value == 0 {
   |            ^^^^^^^^^^^^^^^ use of borrowed `*self`

error[E0503]: cannot use `self.some_value` because it was mutably borrowed
  --> mytest/main/src/main.rs:24:12
   |
21 | impl<'a> Coordinator<'a>{
   |      -- lifetime `'a` defined here
22 |     pub fn main(&'a mut self){
23 |         self.operate();
   |         --------------
   |         |
   |         borrow of `*self` occurs here
   |         argument requires that `*self` is borrowed for `'a`
24 |         if self.some_value == 0 {
   |            ^^^^^^^^^^^^^^^ use of borrowed `*self`
...

我想知道是否有人可以帮助我解决这个问题，谢谢！

Answer 1

首先：我强烈建议您重新考虑您的类型体系结构。为什么void delete_worker_by_id(int id, List *head) { List **previous = &head; List *current = (*previous) -> next; if(head -> next == NULL && (*head).id == id) { free(head); head = NULL; } //if only 1 node in List while((*current).id != id) { *previous = current; current = current -> next; } if((*current).id == id) { (*previous) -> next = current -> next; current -> next = NULL; free(current); return; } puts("No worker with this id"); }和Class是特征？您的不同类是否具有不同的实现细节，例如，一个内部使用School，另一个内部使用Vec？

正如rodrigo在评论中已经指出的那样，您只需删除几个HashMap即可进行编译。原因是，在您的代码中，您实际上是说，'a的可变自我借贷将持续与Coordinator::operate()的可变自我借贷一样长，但是您在那里重新借用了。

然后看起来像这样：

Coordinator::main()

当然，您还必须定义一些实际的结构来实现这些特征，我将举一个例子：

trait Class {
    fn student_count(&self) -> usize;
    fn student_score(&self, i: usize) -> u64;
}

trait School<'a> {
    fn class_count(&self) -> usize;
    fn class(&'a self, i: usize) -> &'a dyn Class;
}

trait ScoreHandler<'a> {
    fn handle(&mut self, school: &'a dyn School<'a>);
}
struct Coordinator<'a> {
    some_value: u64,
    school: &'a dyn School<'a>,
    score_handler: &'a mut dyn ScoreHandler<'a>,
}

impl<'a> Coordinator<'a> {
    pub fn main(&mut self) {
        self.operate();
        if self.some_value == 0 {
            println!("0");
        }
    }
    fn operate(&mut self) {
        self.score_handler.handle(self.school);
    }
}

然后，您的主体可能看起来像这样：

struct ClassA {
    student_scores: Vec<u64>,
}

impl Class for ClassA {
    fn student_count(&self) -> usize {
        self.student_scores.len()
    }
    fn student_score(&self, i: usize) -> u64 {
        self.student_scores[i]
    }
}

struct SchoolA<'a> {
    classes: Vec<&'a dyn Class>,
}

impl<'a> School<'a> for SchoolA<'a> {
    fn class_count(&self) -> usize {
        self.classes.len()
    }
    fn class(&'a self, i: usize) -> &'a dyn Class {
        self.classes[i]
    }
}

struct ScoreHandlerA {
    some_internal_state: u64,
}

impl<'a> ScoreHandler<'a> for ScoreHandlerA {
    fn handle(&mut self, school: &'a dyn School<'a>) {
        for i in 0..school.class_count() {
            println!("Handling a class in a school");
        }
    }
}

锈蚀的寿命相互矛盾

1 个答案: