Function product_by 

pub fn product_by<T, R>(collection: &[T], iteratee: impl Fn(&T) -> R) -> R
where
    R: Mul<Output = R> + From<u8> + Copy,

Calculate the product of values obtained by applying a function to each element in a collection. If the collection is empty, returns 1 (multiplicative identity). Works with any numeric type that implements std::ops::Mul and can be copied.

Arguments

• collection - A slice of items.
• iteratee - A function that takes an item from the collection and returns a number.

Returns

• T - The product of all numbers generated by the iteratee function.

Examples

use lowdash::product_by;

let numbers = vec![1, 2, 3, 4];
let result = product_by(&numbers, |x| x * 2);
assert_eq!(result, 384); // (1*2) * (2*2) * (3*2) * (4*2)

use lowdash::product_by;

#[derive(Debug)]
struct Rectangle {
    width: f64,
    height: f64,
}

let rectangles = vec![
    Rectangle { width: 2.0, height: 3.0 },
    Rectangle { width: 4.0, height: 5.0 },
];

let total_area = product_by(&rectangles, |r| r.width * r.height);
assert_eq!(total_area, 120.0); // (2*3) * (4*5)