The Swift language and its type system incorporate a number of popular language features, including object-oriented programming via classes, function and operator overloading, subtyping, and constrained parametric polymorphism. Swift makes extensive use of type inference, allowing one to omit the types of many variables and expressions.

Protocols in swift defines a blueprint of methods, properties, and other requirements that suit a particular task or piece of functionality. The protocol can then be adopted by a class, structure, or enumeration to provide an actual implementation of those requirements. Any type that satisfies the requirements of a protocol is said to conform to that protocol.

VSDropdown is an iOS drop-in solution which can be used to show dropdown below/above any UIView. This class adapts appearance of the button, for which it is shown, which we can customise, and presents itself with appropriate frame and direction. Irrespective of the button’s hierarchy in the window, the dropdown takes touches everywhere on the screen. It dismisses itself when tapped outside its bounds.