Array extension that insert an element n-times in the array with a gap between each element's insertion.

repeat_array.swift

extension Array
{
    /**
        Insert an element n-times in the array
        with a gap between each element's insertion. 

        ```
        var numbers: [String] = [ "1", "2", "3", "4", "5", "6", "7", "8", "9", "10" ]
        numbers.repeat("X", gap: 3, fromTheBeginning: false)
        ```

        After the `repeat` function `numbers` array will be:

        ```
        ["1", "2", "3", "X", "4", "5", "6", "X", "7", "8", "9", "X", "10"]
        ```

        - Parameters:
            - element: New element 
            - gap: Distance between new element insertions
            - fromTheBeginning: Insert the new element at 0 index.
        - SeeAlso: `repeated(_:gap:fromTheBeginning:)` for non mutating version
    */
    mutating func `repeat`(_ element: Element, gap: Int, fromTheBeginning: Bool = false)
    {
        let indexes: [Int] = (0..<(self.count / gap)).map({ ($0 + 1) * gap }).reversed()
        
        for index in indexes
        {
            self.insert(element, at: index)
        }
        
        if fromTheBeginning
        {
            self.insert(element, at: 0)
        }
    }
    
    /**
        Create a copy of the current array and 
        insert an element n-times in the new array
        with a gap between each element's insertion. 

        ```
        let numbers: [String] = [ "1", "2", "3", "4", "5", "6", "7", "8", "9", "10" ]
        let mixed_numbers: [String] = numbers.repeat("X", gap: 3, fromTheBeginning: false)
        ```

        After the `repeat` function `mixed_numbers` array will be:

        ```
        ["1", "2", "3", "X", "4", "5", "6", "X", "7", "8", "9", "X", "10"]
        ```

        - Parameters:
            - element: New element 
            - gap: Distance between new element insertions
            - fromTheBeginning: Insert the new element at 0 index.
        - SeeAlso: `repeat(_:gap:fromTheBeginning:)` for mutating version
    */
    func repeated(_ element: Element, gap: Int, fromTheBeginning: Bool = false) -> [Element]
    {
        var other: [Element] = [Element](self)
        other.repeat(element, gap: gap, fromTheBeginning: fromTheBeginning)
        
        return other
    }
}