Question

在学习Rust的过程中，我试图为向量的每个元素添加一个整数：

trait Arith: Copy {
    fn add(self, b: Self) -> Self;
    fn mult(self, b: Self) -> Self;
    fn print(self);
}

impl Arith for i32 {
    fn add(self, b: Self) -> Self {
        self + b
    }

    fn mult(self, b: Self) -> Self {
        self * b
    }

    fn print(self) {
        println!("Val = {}", self);
    }
}

fn vec_add<T: Arith>(vec: &mut Vec<T>) {
    for e in vec.iter_mut(){
        /* e is of type &mut i32. But you can give it to print() which
           expects i32 because rust derefs it implicitly */
        e.print();
        e.add(5);
    }
}

fn main() {
    println!("Hello World");
    let mut vec: Vec<i32> = vec![1,2,3,4,5];
    vec_add(&mut vec);
}

但我面临以下问题：

<anon>:33:15: 33:16 error: mismatched types:
 expected `T`,
    found `_`
(expected type parameter,
    found integral variable) [E0308]
<anon>:33         e.add(5);

你能解释一下我在这里犯的错误吗？

Answer 1

数字5是一个整数（我认为它默认为i32或者u32，目前我不记得了）。类型T，它是泛型类型，可以是任何东西，因此通常5不是T的相同类型。您可以强制T为整数，也可以这样更改vec_add：

fn vec_add<T: Arith>(vec: &mut Vec<T>, val: T){
    for e in vec.iter_mut(){
        /* e is of type &mut i32. But you can give it to print() which
           expects i32 because rust derefs it implicitly */
        e.print();
        e.add(val);
    }
}

fn main(){
    println!("Hello World");
    let mut vec: Vec<i32> = vec![1,2,3,4,5];
    vec_add(&mut vec, 5);
}

为泛型类型的向量的每个元素添加一个数字

1 个答案: