fn main() {// 对于Copy类型// 三种等效写法// 1. map(|x| *x)// 2. map(|&x| x)// 3. copied()， 优先使用，结构清晰可读性高，一看就知道发生了复制// 这三种写法，都是在复制元素，如果是非Copy类型将发生所有权转移let arr1 = [1, 2, 3, 4, 5];let vec1: Vec<i32> = arr1.iter().map(|x| *x + 1).collect();let vec2: Vec<i32> = arr1.iter().map(|&x| x * 2).collect();let vec3: Vec<i32> = arr1.iter().copied().filter(|x| x & 1 == 1).collect(); println!("vec1 = {:?}", vec1);println!("vec2 = {:?}", vec2);println!("vec3 = {:?}", vec3);// String不是copy类型let string_arr = ["a".to_string(), "b".to_string(), "c".to_string()];// 编译不通过// let vec4: Vec<String> = str_arr.iter().copied().collect(); // cannot move out of `*x` which is behind a shared reference// move occurs because `*x` has type `String`, which does not implement the `Copy` trait// let vec4: Vec<String> = str_arr.iter().map(|x| *x).collect();// move occurs because `x` has type `String`, which does not implement the `Copy` // let vec4: Vec<String> = str_arr.iter().map(|&x| x).collect();let vec4: Vec<String> = string_arr.iter().cloned().collect();let vec4: Vec<String> = string_arr.iter().map(|x| x.clone()).collect();// cloned() 创建了全新的String对象，闭包参数x是局部变量，不是引用，拥有所有权// cannot return value referencing function parameter `x`// returns a value referencing data owned by the current function// let vec5: Vec<&str> = str_arr.iter().cloned().map(|x| x.as_str()).collect();let str_arr = ["a", "b", "c"];// 所有不可变引用 &T都实现了 Copytrait，无论 T是什么类型。let vec5: Vec<&str> = str_arr.iter().map(|&x| x).collect();}