rust - 模式匹配 float 的替代方案是什么？

Question

Rust 已决定在模式中禁止浮点字面值:Matching on floating-point literal values is totally allowed and shouldn't be #41255 .目前它是一个警告，但在未来的版本中将是一个硬错误。

如何实现以下代码的无警告等效项？

struct Point {
    x: f64,
    y: f64,
}

let point = Point { x: 5.0, y: 4.0 };

match point {
    Point { x: 5.0, y } => println!("y is {} when x is 5", y),
    _ => println!("x is not 5"),
}

warning: floating-point types cannot be used in patterns
  --> src/main.rs:10:20
   |
10 |         Point { x: 5.0, y } => println!("y is {} when x is 5", y),
   |                    ^^^
   |
   = note: `#[warn(illegal_floating_point_literal_pattern)]` on by default
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #41620 <https://github.com/rust-lang/rust/issues/41620>

现在不可能了吗？我需要改变我对模式的看法吗？还有其他匹配方式吗？

Answer 1

你可以使用比赛后卫:

match point {
    Point { x, y } if x == 5.0 => println!("y is {} when x is 5", y),
    _ => println!("x is not 5"),
}

这会将责任推回给您，因此不会产生任何类型的警告。

Floating point equality is an interesting subject though ...所以我建议您进一步研究它，因为它可能是错误的来源(我想这是 Rust 核心团队不想匹配浮点值的原因)。