Combine arrays

Programming languages have many syntaxes for combining 2 arrays. In Swift we use the plus operator. We can also append many elements (in an array) at once.

And with append contentsOf, we can add arrays to arrays with a more verbose syntax. This can make some programs clearer and may be preferred.

First example

Here we merge 2 arrays with an addition expression. We can use array variable names (like "numbers") or place the array expression directly in the addition statement.

let numbers = [10, 20, 30]
let numbers2 = [1, 2, 3]

// Combine the two arrays into a third array.
// ... The first 2 arrays are not changed.
let combined = numbers + numbers2
print(combined)
[10, 20, 30, 1, 2, 3]

Add many elements

Sometimes we want to append two or more elements to an array at once. We can use an addition expression for this purpose.

// This must be a var.
var colors = ["red"]

// Add two elements to the array.
// ... The arrays are combined.
colors += ["orange", "blue"]

// Add more elements.
colors += ["silver", "gold"]
print(colors)
["red", "orange", "blue", "silver", "gold"]

Append, contentsOf

With this method, we add the elements of one array to another. This has the same effect as the plus operator expressions. But it uses a normal method call.

var animals = ["cat"]
var animals2 = ["bird", "fish", "dog"]

// Add the second array to the first.
// ... This is like using the "add" operator.
animals.append(contentsOf: animals2)
print(animals)
["cat", "bird", "fish", "dog"]

In Swift we can use a plus to combine two arrays. But the append() method is also worth using as it may be clearer to understand in some programs.