4.3 rust func closure

fn  add_one_v1   (x: u32) -> u32 { x + 1 }
let add_one_v2 = |x: u32| -> u32 { x + 1 };
let add_one_v3 = |x|             { x + 1 };
let add_one_v4 = |x|               x + 1  ;

pub fn test3() {
    let example_closure = |x| x;

    let s = example_closure(String::from("hello"));
    let n = example_closure(5);
}

  --> src/base/k_closure.rs:53:29
   |
53 |     let n = example_closure(5);
   |                             ^
   |                             |
   |                             expected struct `String`, found integer
   |                             help: try using a conversion method: `5.to_string()`

The first time we call example_closure with the String value, the compiler infers the type of x and the return type of the closure to be String. Those types are then locked into the closure in example_closure, and we get a type error if we try to use a different type with the same closure.

不换数据类型,下面的是正确的

pub fn test3() {
    let example_closure = |x| x;

    let s = example_closure(6);
    println!("{}",s);
    let n = example_closure(5);
    println!("{}",n);
}

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5