在阅读Rust Book中有关智能指针.

We could change the definition of Cons to hold references instead, but then we would have to specify lifetime parameters. By specifying lifetime parameters, we would be specifying that every element in the list will live at least as long as the entire list. The borrow checker wouldn’t let us compile let a = Cons(10, &Nil); for example, because the temporary Nil value would be dropped before a could take a reference to it.

rust

#[derive(Debug)]
enum List<'a> {
    Cons(i32, &'a List<'a>),
    Nil,
}
use crate::List::{Cons, Nil};

fn main() {
    let a = Cons(10, &Nil);
    println!("{:?}", a);
    let a = Cons(5, &Cons(10, &Nil));
    println!("{:?}", a);
    let b = Cons(3, &a);
    println!("{:?}", b);
    {
        let c = Cons(4, &a);
        println!("{:?}", c);
    }
}

复现代码并没有出现错误提示,就有些疑惑.

最后发现是在这个提议¹中,将常量表达式提升为静态变量.

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