使用 Any 时如何处理“类型不满足所需的生命周期”？

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。 这是代码的操场链接

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？ 学习语言真是令人沮丧。

Answer 1

主要问题是Function中定义的as_any方法。 如果您查看文档中的Any特征定义，您会看到该特征的生命周期为'static 。 Function中的params字段的生命周期为'a ，其生命周期不如'static的生命周期。 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命周期，但如果没有进一步的上下文，很难说。