Function flatten 

pub fn flatten<T, Slice>(collection: &[Slice]) -> Vec<T>
where
    Slice: AsRef<[T]>,
    T: Clone,

Flatten a collection of slices into a single vector, preserving the order of elements.

This function takes a slice of slices and concatenates all inner slices into a single Vec<T>. The order of elements is preserved based on their original ordering in the input collection.

Time Complexity:
O(n), where n is the total number of elements across all inner slices.

Arguments

• collection - A slice of slices to be flattened.

Type Parameters

• T - The type of elements in the slices. Must implement Clone.
• Slice - The type of the inner slices. Must implement AsRef<[T]>.

Returns

• Vec<T> - A vector containing all elements from the input slices, flattened into a single collection.

Examples

use lowdash::flatten;

let nested = vec![vec![1, 2], vec![3, 4], vec![5]];
let flat = flatten(&nested);
assert_eq!(flat, vec![1, 2, 3, 4, 5]);

use lowdash::flatten;

#[derive(Debug, PartialEq, Clone)]
struct Person {
    name: String,
    age: u32,
}

let people_groups = vec![
    vec![
        Person { name: "Alice".to_string(), age: 25 },
        Person { name: "Bob".to_string(), age: 30 },
    ],
    vec![
        Person { name: "Carol".to_string(), age: 35 },
        Person { name: "Dave".to_string(), age: 40 },
    ],
];

let flat_people = flatten(&people_groups);
assert_eq!(
    flat_people,
    vec![
        Person { name: "Alice".to_string(), age: 25 },
        Person { name: "Bob".to_string(), age: 30 },
        Person { name: "Carol".to_string(), age: 35 },
        Person { name: "Dave".to_string(), age: 40 },
    ]
);