特征对象的静态数组 [英] static array of trait objects

问题描述

是否可以定义特征对象的静态数组:

Is it possible to define static array of trait objects:

#[macro_use]
extern crate lazy_static;

trait Tr {}

struct A {}
impl Tr for A {}

struct B {}
impl Tr for B {}

lazy_static! {
    static ref ARR: [Box<dyn Tr>;2] = [Box::new(A {}), Box::new(B {})];
    // error[E0277]: `(dyn Tr + 'static)` cannot be shared between threads safely
}

而不是每个 Test 实例有一个 _arr:

Instead of having one _arr per each Test instance:

struct Test {
    arr: [Box<dyn Tr>; 2],
}

impl Default for Test {
    fn default() -> Test {
        Test {
            arr: [Box::new(A {}), Box::new(B {})],
        }
    }
}

推荐答案

你想要Box:

#[macro_use]
extern crate lazy_static;

trait Tr {}

struct A {}
impl Tr for A {}

struct B {}
impl Tr for B {}

lazy_static! {
    static ref ARR: [Box<dyn Tr + Sync>; 2] = [Box::new(A {}), Box::new(B {})];
}

来自Sync:

可以安全地在线程之间共享引用的类型.

Types for which it is safe to share references between threads.

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