我可以用局部变量来影响const绑定吗？

Question

我认为这会奏效:

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:

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)

这有效:

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

这样做:

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

我做错了什么,或者是否不可能const用let同名的名字遮蔽现有的绑定？

Answer 1

我想我明白了...当我使用时let SOME_CONST,编译器认为我是模式匹配.

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

好像我已经x在程序中完成所有操作并将它们扩展为常量10:

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