swiftにはassertさせる関数がいっぱいあって困ります。 1) assert() let ary = [1, 2, 3] let i = 3 assert(i < ary.count) print("\(ary[i])") assertion failed: file /develop/aaa/aaa/ViewController.swift, line 18 2) precondition() let ary = [1, 2,…