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 
    }
}

当我尝试编译以上代码时，出现以下错误。这是代码的操场 link

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struct的生存期感到困惑，因为我只是返回self。它还希望生命周期是“静态的”。学习语言实在令人沮丧。

Answer 1

主要问题是在as_any中定义的Function方法。如果查看documentation中的Any特性定义，您将看到该特性的生命周期范围为'static。 params中的Function字段的生存期为'a，生存期不会长于'static的生存期。一种解决方案是将params字段定义为Box<Vec<Box<String>>>，而不是使用引用并定义生存期，但是如果没有进一步的上下文，这很难说。