2つの配列の要素すべての組み合わせを出力 (swift) #CodePiece

CodePiece.swift

import Foundation
func combine<E1, E2>(_ arr1: [E1], _ arr2: [E2]) -> [(E1, E2)] {
    guard !arr1.isEmpty && !arr2.isEmpty else {
        return []
    }
    func _c(_ e1: E1, _ arr2: [E2]) -> [(E1, E2)] {
        return arr2.map{(e1, $0)}
    }
    return _c(arr1[0], arr2) + combine(arr1.dropFirst().map{$0}, arr2)
}
print(combine([1,2,3], ["a", "b"]))
print(combine([1], ["a", "b"]))