RangeReplaceableCollection

Range-replaceable collections provide operations that insert and remove elements. For example, you can add elements to an array of strings by calling any of the inserting or appending operations that the RangeReplaceableCollection protocol defines.

var bugs = ["Aphid", "Damselfly"]
bugs.append("Earwig")
bugs.insert(contentsOf: ["Bumblebee", "Cicada"], at: 1)
print(bugs)
// Prints "["Aphid", "Bumblebee", "Cicada", "Damselfly", "Earwig"]"

Likewise, RangeReplaceableCollection types can remove one or more elements using a single operation.

bugs.removeLast()
bugs.removeSubrange(1...2)
print(bugs)
// Prints "["Aphid", "Damselfly"]"

bugs.removeAll()
print(bugs)
// Prints "[]"

Lastly, use the eponymous replaceSubrange(_:with:) method to replace a subrange of elements with the contents of another collection. Here, three elements in the middle of an array of integers are replaced by the five elements of a Repeated<Int> instance.

 var nums = [10, 20, 30, 40, 50]
 nums.replaceSubrange(1...3, with: repeatElement(1, count: 5))
 print(nums)
 // Prints "[10, 1, 1, 1, 1, 1, 50]"

Conforming to the RangeReplaceableCollection Protocol

To add RangeReplaceableCollection conformance to your custom collection, add an empty initializer and the replaceSubrange(_:with:) method to your custom type. RangeReplaceableCollection provides default implementations of all its other methods using this initializer and method. For example, the removeSubrange(_:) method is implemented by calling replaceSubrange(_:with:) with an empty collection for the newElements parameter. You can override any of the protocol’s required methods to provide your own custom implementation.