matrix.swift

struct Matrix<Element> {
    let dimensions: [Int]
    var content: [Element]

    init(_ dimensions: [Int], initial value: Element) {
        self.dimensions = dimensions
        let elementCount = self.dimensions.reduce(1, *)
        self.content = [Element](repeatElement(value, count: elementCount))
    }

    func index(of indexes: [Int]) -> Int {
        // To access [w][x][y][z] in matrix[a][b][c][d], the index is 
        // w*d*c*b + x*d*c + y*d + z
        let reversedDimensions = Array(self.dimensions.reversed())
        let dimensionLevels = (0..<(reversedDimensions.count-1)).map {
            reversedDimensions[($0+1)..<reversedDimensions.count]
        }
        return zip(indexes, dimensionLevels).map { $1.reduce($0, *) }.reduce(indexes.last!, +)
    }

    subscript(indexes: Int...) -> Element {
        get {
            return self.content[self.index(of: indexes)]
        }
        set {
            self.content[self.index(of: indexes)] = newValue
        }
    }
}

extension Matrix where Element: ExpressibleByIntegerLiteral {
    init(_ dimensions: [Int]) {
        self.init(dimensions, initial: 0)
    }
}

var matrix32 = Matrix<Int>([3, 2])
matrix32[0, 1] = 5
matrix32[1, 0] = 7
print(matrix32.content)