scalar_map

map 用于标量类型。

let num: Option<i32> = Some(42);
assert_eq!(num.map(|x| 42 - x), Some(0));

let num: i32 = 42;
assert_eq!(num.map(|x| 42 - x), 0);

let num: Option<i32> = Some(42);
assert_eq!(num.and_then(Option::Some), Some(0));

let num: i32 = 42;
assert_eq!(num.and_then(Option::Some), Some(0));

解决什么问题

• 即使在将 Option 重新构建的情况下，您仍然可以保留 map 和 and_then。

• 您想要

  x.map(Mutex::new).map(Arc::new)
  

  ...而不是

  Arc::new(Mutex::new(x))
  

自定义结构体

派生

# Run this to add the `derive` feature
cargo add scalar_map --features derive

#[derive(Debug, PartialEq, ScalarMap)]
struct MyNum(i32);

let num = MyNum(42);
assert_eq!(num.map(|x| 42 - x.0).map(MyNum), MyNum(0));

不派生

#[derive(Debug, PartialEq)]
struct MyNum(i32);
impl ScalarMapExt for MyNum {}

let num = MyNum(42);
assert_eq!(num.map(|x| 42 - x.0).map(MyNum), MyNum(0));