Use flatMap with multiple optional variables, ensuring all are non-nil before making a function call.

MultidimensionalOptionalFlatMap.swift

func flatMap<U, V, T>(_ i: U?, _ j: V?, block: (U, V)->T) -> T? {
    var result: T?
    if let i = i, let j = j { result = block(i,j) }
    return result
}

func flatMap<U, V, W, T>(_ i: U?, _ j: V?, _ k: W?, block: (U, V, W)->T) -> T? {
    var result: T?
    if let i = i, let j = j, let k = k { result = block(i,j,k) }
    return result
}


let i: Int? = 1
let j: Int? = 2
var k: Int?
let m: Int? = flatMap(i, j) { max($0, $1) }                     // i and j non-nil, so will execute
let n: Int? = flatMap(i, j, k) { $0+$1+$2 }                     // k is nil. Won't execute
flatMap(i,j) { print("i and j are non-nil: \($0) and \($1)") }  // Will execute. No return