Using RangeReplaceableCollectionType

Hotel.swift

//: Playground - noun: a place where people can play

struct Room: IntegerLiteralConvertible {
    let number: Int
    
    init(integerLiteral value: Int) {
        number = value
    }
}

extension Room: CustomStringConvertible {
    var description: String { return "#\(number)" }
}

struct Hotel {
    private var rooms: [Room] = []
}

extension Hotel: CollectionType {
    var startIndex: Int { return 0 }
    var endIndex:   Int { return rooms.count }
    
    subscript (index: Int) -> Room {
        precondition(index >= 0 && index < endIndex, "No room at \(index)")
        return rooms[index]
    }
}

extension Hotel: RangeReplaceableCollectionType {
    mutating func reserveCapacity(n: Int.Distance) { }
    
    mutating func replaceRange<C : CollectionType where C.Generator.Element == Room>(subRange: Range<Int>, with newElements: C) {
        rooms.replaceRange(subRange, with: newElements)
    }
}

var hotel = Hotel(rooms: [2, 4, 12])
hotel.append(4)