自作クラス、構造体の \(), print() をカスタマイズする ref: http://qiita.com/ezura/items/8f31b14bd1418a0dab81

Printable,DebugPrintable実装時

class DescriptionSample: Printable, DebugPrintable {
    var m = "sample"
    // Printable
    var description: String {
        return "\(m) description"
    }
    // DebugPrintable
    var debugDescription: String {
        return "\(m) debugDescription"
    }
}

let b = DescriptionSample()
print(b)      // "sample description\n"
debugPrint(b) // "sample debugDescription\n"
"\(b)"        // "sample description"

通常

class NormalClass {
  var m = "sample"
}

let a = NormalClass()
print(a)      // NormalClass\n
debugPrint(a) // NormalClass\n
"\(a)"        // "NormalClass"