Tips on Using Swift Collections

4 Feb 2022

Most people working with Swift will be familiar with at least 2 collections: Array and Set. But it might not be clear that there are other collections being used, such as String and LazyCollection.

Indices

Lazy

Lazy can be very useful and aid with performance, but note that it can also hurt performance.

LazyCollection has extra overhead, but it can help when you might not need to iterate over the full collection.

For example take this:

let mixedArray: [Any] = [
  0,
  "1",
  [
    "0",
    1,
  ],
  3.0,
]

let firstInteger = mixedArray.compactMap { $0 as? Int }.first

TODO: Make custom iterator to demonstrait.

This will iterate over our entire array, check the type of every element, and then check if the resulting array has an element.

Using lazy means we can stop early:

let mixedArray: [Any] = [
  0,
  "1",
  [
    "0",
    1,
  ],
  3.0,
]

let firstInteger = mixedArray.lazy.compactMap { $0 as? Int }.first