1> ["1", "two", "10"].compactMap { Int($0) }                 //=> [1, 10]
2> ["1", "two", "10"].compactMap(Int.init)                   //=> [1, 10]
3> ["1", "two", "10"].map { $0[...] }.compactMap { Int($0) } //=> [1, 10]
4> ["1", "two", "10"].map { $0[...] }.compactMap(Int.init)   //=> [0, 0, 0]