import _Differentiation

let values: [[Double]] = [[0, 0], [0, 0]]
let const = 1.12345
let result = add(const, to: values)

@differentiable(reverse)
func add(_ const: Double, to values: [[Double]]) -> [[Double]] {
    var result = values
    for i in withoutDerivative(at: values.indices) {
        for j in withoutDerivative(at: values.indices) {
            result.updated(at: i, j, with: values[i][j] + const)
        }
    }
    return result
}

extension Array where Element == [Double] {
    @differentiable(reverse)
    mutating func updated(at i: Int, _ j: Int, with newValue: Double) {
        self[i][j] = newValue
    }
 
    @derivative(of: updated)
    mutating func vjpUpdated(at i: Int, _ j: Int, with newValue: Double)
    -> (value: Void, pullback: (inout TangentVector) -> (Double.TangentVector)) {
        self.updated(at: i, j, with: newValue)

        func pullback(dSelf: inout TangentVector) -> (Double.TangentVector) {
            let dElement = dSelf[i][j]
            dSelf.base[i].base[j] = 0
            return dElement
        }
        let value: Void = ()

        return (value, pullback)
    }
}