Rust编译错误E0515：无法返回临时值引用的解决方案求助

我尝试用静态值实例化结构体，但编译器提示创建了临时值，所有引用均为static，问题与rust-lang/rust#69574一致。以下是代码及编译错误信息，求修复或规避方法：

代码示例 #

struct OutputDescription {
    name: &'static str,
}

struct SubOutput<T> {
    sub_param_a: T,
}

struct Output {
    param_a: SubOutput<bool>
}

impl <T: Description>Description for SubOutput<T> {
    fn name() -> &'static str {
        "param_a"
    }

    fn fields() -> &'static [OutputDescription] {
        &[OutputDescription {
            name: T::name(),
        }]
    }
}

trait Description {
    fn name() -> &'static str;

    fn fields() -> &'static [OutputDescription];
}

编译错误信息 #

Compiling playground v0.0.1 (/playground)
error[E0515]: cannot return reference to temporary value
  --> src/main.rs:19:9
   |
19 |            &[OutputDescription {
   |   _________^-
   |  |_________|
   | ||
20 | ||             name: T::name(),
21 | ||         }]
   | ||          ^
   | ||__________|
   |  |__________returns a reference to data owned by the current function
   |             temporary value created here

For more information about this error, try `rustc --explain E0515`.
error: could not compile `playground` (bin "playground") due to previous error

错误原因 #

直接返回&[OutputDescription { ... }]时，这个数组是函数栈上的临时值，生命周期仅存在于函数调用期间。函数返回后临时值会被销毁，因此编译器不允许返回其引用——哪怕数组内的字段都是&'static str，数组本身的生命周期也不满足'static要求。

修复方案 #

方案一：使用编译期静态常量数组 #

如果T::name()是编译期可确定的静态值，可以将数组定义为static常量，直接返回其引用：

struct OutputDescription {
    name: &'static str,
}

struct SubOutput<T> {
    sub_param_a: T,
}

struct Output {
    param_a: SubOutput<bool>
}

trait Description {
    fn name() -> &'static str;
    fn fields() -> &'static [OutputDescription];
}

impl <T: Description>Description for SubOutput<T> {
    fn name() -> &'static str {
        "param_a"
    }

    fn fields() -> &'static [OutputDescription] {
        // 定义编译期静态数组
        static FIELDS: [OutputDescription; 1] = [OutputDescription {
            name: T::name(),
        }];
        &FIELDS
    }
}

方案二：使用lazy_static延迟初始化 #

如果需要运行期动态生成数组（或T::name()非编译期常量），可以借助lazy_static crate实现线程安全的静态延迟初始化：

1. 先在Cargo.toml添加依赖：

[dependencies]
lazy_static = "1.4.0"

2. 修改代码：

use lazy_static::lazy_static;

struct OutputDescription {
    name: &'static str,
}

struct SubOutput<T> {
    sub_param_a: T,
}

struct Output {
    param_a: SubOutput<bool>
}

trait Description {
    fn name() -> &'static str;
    fn fields() -> &'static [OutputDescription];
}

impl <T: Description>Description for SubOutput<T> {
    fn name() -> &'static str {
        "param_a"
    }

    fn fields() -> &'static [OutputDescription] {
        lazy_static! {
            static ref FIELDS: Vec<OutputDescription> = vec![OutputDescription {
                name: T::name(),
            }];
        }
        FIELDS.as_slice()
    }
}

lazy_static会在第一次访问FIELDS时完成初始化，确保变量生命周期为'static，同时保证线程安全。

内容的提问来源于stack exchange，提问作者felix