Explain the concept of lazy collections and their use in programming.

Lazy collections are collections whose elements are computed or loaded on demand, rather than immediately upon creation. This approach saves resources and improves performance, especially when working with large data sets.

In programming, lazy collections are often implemented using lazy sequences or generators that do not store all elements in memory but generate them on the fly during iteration.

For example, in Swift, you can use lazy sequences as follows:

let numbers = [1, 2, 3, 4, 5]
let lazySquares = numbers.lazy.map { $0 * $0 }

for square in lazySquares {
    print(square)
}

Here, lazy indicates that the squares are computed only during iteration, not immediately for the entire array. This is useful if you plan to process only part of the collection or want to delay heavy computations.