↓の中にはなさそう？
<stdin>:4:9: note: overloads for '+' exist with these partially matching parameter lists: (Array<Element>, Array<Element>), (CGFloat, CGFloat), (Date, TimeInterval), (Decimal, Decimal), (DispatchTime, DispatchTimeInterval), (DispatchTime, Double), (DispatchWallTime, DispatchTimeInterval), (DispatchWallTime, Double), (Double, Double), (Float, Float), (Float80, Float80), (IndexPath, IndexPath), (Int, Int), (Int16, Int16), (Int32, Int32), (Int64, Int64), (Int8, Int8), (Measurement<UnitType>, Measurement<UnitType>), (Other, Self), (Self, Other), (Self, Self.Scalar), (Self, Self.Stride), (Self.Scalar, Self), (Self.Stride, Self), (String, String), (UInt, UInt), (UInt16, UInt16), (UInt32, UInt32), (UInt64, UInt64), (UInt8, UInt8)