rust - 如何将多个args传递给rust封闭-预期的封闭需要1个参数

Question

我是闭包新手，但我不明白为什么会收到以下错误。

如果我不包括第二个参数，那么它的工作原理是:

fn obj_x(x: Vec<f64>) -> f64 {
    return 0.0;
};

let f = |x: &Vec<f64>| obj_x(x.to_vec());

这是我的封信:

fn foo() {
    let f = |x: &Vec<f64>, N: usize| obj_x(x.to_vec(), N);
}

fn obj_x(x: Vec<f64>, N: usize) -> f64 {
    let x = (x[0] + 4.0).powf(2.0);

    return x;
}

但不幸的是它失败了

error[E0593]: closure is expected to take 1 argument, but it takes 2 arguments
   --> src/main.rs:120:44
    |
114 |     let f = |x: &Vec<f64>, N: usize | obj_x(x.to_vec(),N);
    |             ------------------------- takes 2 arguments
...
120 |         let mut fmin = Funcmin::new(&mut x,&f,&g,"cg");
    |                                            ^^ expected closure that takes 1 argument
    |

这是我的完整代码:

fn obj_x(x: Vec<f64>, N: usize) -> f64 {
    let x = (x[0] + 4.0).powf(2.0);

    return x;
}

fn gradient_x(x: Vec<f64>) -> Vec<f64> {
    return vec![2.0 * (x[0] + 4.0)];
}

fn test() {
    let f = |x: &Vec<f64>, &N: usize| obj_x(x.to_vec(), N);
    let g = |x: &Vec<f64>| gradient_x(x.to_vec());
    let mut x = vec![40.0f64];
    let mut N = 2220;
    {
        //you must create a mutable object
        let mut fmin = Funcmin::new(&mut x, &f, &g, "cg");
        fmin.minimize();
    }
    println!("{:?}", x);
}

Answer 1

此解决方案对我有用:声明
fn fold(n: u32, init: u32, op: impl Fn(u32, u32) -> u32) -> u32 {...
并称其为
fold(n, 1, |x: u32, y: u32| -> u32 {x + y })