这是我试图返回对结构的字段的可变引用。
pub trait Objective {
fn get_children<'a>(&'a mut self) -> &'_ mut Vec<&'_ mut Box<dyn Objective>>;
fn get_parent(&'_ mut self) -> &'_ mut Box<dyn Objective>;
fn update(&'_ self) -> ();
}
// #[derive(Objective)]
pub struct Object<'a> {
children: Vec<&'a mut Box<dyn Objective>>,
parent: &'a mut Box<dyn Objective>,
}
impl<'a> Objective for Object<'a> {
fn get_children(&'a mut self) -> &'_ mut Vec<&'_ mut Box<dyn Objective>> {
return &mut self.children;
}
fn get_parent(&'_ mut self) -> &'_ mut Box<dyn Objective> {
return self.parent;
}
fn update(&'_ self) -> () {}
}
寿命有问题。以下是编译器给出的错误：
error[E0308]: method not compatible with trait
--> src/lib.rs:14:5
|
14 | fn get_children(&'a mut self) -> &'_ mut Vec<&'_ mut Box<dyn Objective>> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
|
= note: expected fn pointer `fn(&'a mut Object<'a>) -> &'a mut std::vec::Vec<&'a mut std::boxed::Box<(dyn Objective + 'static)>>`
found fn pointer `fn(&'a mut Object<'a>) -> &'a mut std::vec::Vec<&'a mut std::boxed::Box<(dyn Objective + 'static)>>`
note: the lifetime `'a` as defined on the method body at 14:5...
--> src/lib.rs:14:5
|
14 | fn get_children(&'a mut self) -> &'_ mut Vec<&'_ mut Box<dyn Objective>> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
note: ...does not necessarily outlive the lifetime `'a` as defined on the impl at 13:6
--> src/lib.rs:13:6
|
13 | impl<'a> Objective for Object<'a> {
| ^^
error[E0308]: method not compatible with trait
--> src/lib.rs:14:5
|
14 | fn get_children(&'a mut self) -> &'_ mut Vec<&'_ mut Box<dyn Objective>> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
|
= note: expected fn pointer `fn(&'a mut Object<'a>) -> &'a mut std::vec::Vec<&'a mut std::boxed::Box<(dyn Objective + 'static)>>`
found fn pointer `fn(&'a mut Object<'a>) -> &'a mut std::vec::Vec<&'a mut std::boxed::Box<(dyn Objective + 'static)>>`
note: the lifetime `'a` as defined on the impl at 13:6...
--> src/lib.rs:13:6
|
13 | impl<'a> Objective for Object<'a> {
| ^^
note: ...does not necessarily outlive the lifetime `'a` as defined on the method body at 14:5
--> src/lib.rs:14:5
|
14 | fn get_children(&'a mut self) -> &'_ mut Vec<&'_ mut Box<dyn Objective>> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
这是我之前的尝试，我没有明确指定生存期：
pub trait Objective {
fn get_children(&'_ mut self) -> &'_ mut Vec<&'_ mut Box<dyn Objective>>;
fn get_parent(&'_ mut self) -> &'_ mut Box<dyn Objective>;
fn update(&'_ self) -> ();
}
// #[derive(Objective)]
pub struct Object<'a> {
children: Vec<&'a mut Box<dyn Objective>>,
parent: &'a mut Box<dyn Objective>,
}
impl Objective for Object<'_> {
fn get_children(&'_ mut self) -> &'_ mut Vec<&'_ mut Box<dyn Objective>> {
return &mut self.children;
}
fn get_parent(&'_ mut self) -> &'_ mut Box<dyn Objective> {
return self.parent;
}
fn update(&'_ self) -> () {}
}
我也得到了一个类似的错误：
error[E0308]: mismatched types
--> src/lib.rs:15:16
|
15 | return &mut self.children;
| ^^^^^^^^^^^^^^^^^^ lifetime mismatch
|
= note: expected mutable reference `&mut std::vec::Vec<&mut std::boxed::Box<(dyn Objective + 'static)>>`
found mutable reference `&mut std::vec::Vec<&mut std::boxed::Box<(dyn Objective + 'static)>>`
note: the anonymous lifetime #1 defined on the method body at 14:5...
--> src/lib.rs:14:5
|
14 | / fn get_children(&'_ mut self) -> &'_ mut Vec<&'_ mut Box<dyn Objective>> {
15 | | return &mut self.children;
16 | | }
| |_____^
note: ...does not necessarily outlive the lifetime `'_` as defined on the impl at 13:27
--> src/lib.rs:13:27
|
13 | impl Objective for Object<'_> {
| ^^
我该如何解决这个问题？
指定特征的生存期，它就起作用了：
pub trait Objective<'a> {
fn get_children(&mut self) -> &mut Vec<&'a mut Box<dyn Objective<'a>>>;
fn get_parent(&mut self) -> &mut Box<dyn Objective<'a>>;
fn update(&self) -> ();
}
// #[derive(Objective)]
pub struct Object<'a> {
children: Vec<&'a mut Box<dyn Objective<'a>>>,
parent: Box<dyn Objective<'a>>,
}
impl<'a> Objective<'a> for Object<'a> {
fn get_children(&mut self) -> &mut Vec<&'a mut Box<dyn Objective<'a>>> {
&mut self.children
}
fn get_parent(&'_ mut self) -> &mut Box<dyn Objective<'a>> {
&mut self.parent
}
fn update(&'_ self) -> () {}
}
通过指定Objective的生存期，我们可以确保实现者将返回一个由可变引用组成的Vec，该引用满足与特性所需的生存期相同的生存期要求。