我可以用局部变量隐藏 const 绑定吗？

Question

我认为这行得通：

const x: &str = "10";            // declare a const
let x: i32 = x.parse().unwrap(); // reuse the same name for a let binding
assert_eq!(10, x);

但是：

error[E0308]: mismatched types
 --> src/main.rs:3:9
  |
3 |     let x: i32 = x.parse().unwrap(); // reuse the same name for a let binding
  |         ^ expected i32, found reference
  |
  = note: expected type `i32`
             found type `&'static str`

error[E0277]: the trait bound `{integer}: std::cmp::PartialEq<&str>` is not satisfied
 --> src/main.rs:4:5
  |
4 |     assert_eq!(10, x);
  |     ^^^^^^^^^^^^^^^^^^ can't compare `{integer}` with `&str`
  |
  = help: the trait `std::cmp::PartialEq<&str>` is not implemented for `{integer}`
  = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

这个有效：

const x: &str = "10";
let y: i32 = x.parse().unwrap();
assert_eq!(10, y);

这也是：

let x: &str = "10";
let x: i32 = x.parse().unwrap();
assert_eq!(10, x);

我是不是做错了什么，还是无法用同名的 let 隐藏现有的 const 绑定？

Answer 1

我想我明白了...当我使用 let SOME_CONST 时，编译器认为我在进行模式匹配。

当我修复类型时：

const x: i32 = 10;
let x: i32 = x + 1;
assert_eq!(11, x);

我得到一个不同的错误：

error[E0005]: refutable pattern in local binding: `_` not covered
 --> src/main.rs:3:9
  |
3 |     let x: i32 = x + 1;
  |         ^ interpreted as a constant pattern, not new variable

就好像我把程序中所有出现的 x 都取出来并将它们扩展为常量 10:

let 10: i32 = 10 + 1;
assert_eq!(11, x);

我可以用局部变量隐藏 const 绑定吗？

Can I shadow a const binding with a local variable?

rust

constants

let