rust - 使用Any时如何处理 "the type does not fulfill the required lifetime"？

Question

use std::any::Any;

pub enum ObjectType {
    Error,
    Function,
}

pub trait Object {
    fn obj_type(&self) -> ObjectType;

    // Required to downcast a Trait to specify structure
    fn as_any(&self) -> &dyn Any;
}

#[derive(Debug)]
pub struct Function<'a> {
    params: &'a Box<Vec<Box<String>>>,
}

impl<'a> Object for Function<'a> {
    fn obj_type(&self) -> ObjectType {
        ObjectType::Function
    }

    fn as_any(&self) -> &dyn Any { 
        self 
    }
}

当我尝试编译上述代码时，出现以下错误。这里是 Playground link到代码

Compiling playground v0.0.1 (/playground)
error[E0477]: the type `Function<'a>` does not fulfill the required lifetime
  --> src/lib.rs:27:9
   |
27 |         self 
   |         ^^^^
   |
   = note: type must satisfy the static lifetime

error[E0495]: cannot infer an appropriate lifetime due to conflicting requirements
  --> src/lib.rs:27:9
   |
27 |         self 
   |         ^^^^
   |
note: first, the lifetime cannot outlive the lifetime `'a` as defined on the impl at 21:7...
  --> src/lib.rs:21:7
   |
21 | impl <'a>Object for Function<'a> {
   |       ^^
note: ...so that the type `Function<'a>` will meet its required lifetime bounds
  --> src/lib.rs:27:9
   |
27 |         self 
   |         ^^^^
   = note: but, the lifetime must be valid for the static lifetime...
note: ...so that the expression is assignable
  --> src/lib.rs:27:9
   |
27 |         self 
   |         ^^^^
   = note: expected `&(dyn Any + 'static)`
              found `&dyn Any`

为什么 Rust 编译器对结构生命周期感到困惑，因为我只是返回 self.它还希望生命周期是“静态的”吗？学习这门语言真是令人沮丧。

Answer 1

主要问题是as_any Function中定义的方法。如果你看Any documentation 中的特征定义，您将看到该特征的生命周期界限为 'static 。 params领域 Function生命周期为'a它的生命周期不会像 'static 的生命周期那么长。一种解决方案是定义 params字段为Box<Vec<Box<String>>> ，而不是使用引用并定义生命周期，但在没有进一步上下文的情况下，很难说。