Size Classes are an abstraction of how a device should be categorized depending on its screen dimensions. Apple defined two categorizations for both vertical and horizontal sizes called “Regular” and “Compact”. The former specifies a big space, while the latter specifies a small” space. How big or small exactly? Here, “big” and “small” are not intended to be measured in inches. iOS Size Classes Apple has introduced many devices like iPhone, iPad with different screen sizes and resolution. Also after iOS 8 apple has supported multitasking in iPad. So for the developers to develop a common or single UI for all the devices apple has introduced the concept of an adaptive layout by combining auto layout and size classes. What is adaptive layout: The adaptive layout is a method of building the apps based on the size and characteristics of the container instead of a targeting a particular device. We can create a single layout to work on all devices instead of
Enums An enum is considered as a structured data type that can be modified without needing to change say a String or Int multiple times within your code, for example the below shows how easy it would be to change something by accident and forget to change it somewhere else. let myString = "test" if myString == "ttest" { // Doesn't execute because "ttest" is the value assigned to "myString" } With a enum we can avoid this and never have to worry about changing the same thing more than once enum MyEnum : String { case Test = "test" } let enumValue = MyEnum . Test if enumValue == MyEnum . Test { // Will execute because we can reassign the value of "MyEnum.Test" unless we do so within "MyEnum" } Structs I'm not sure how much you know about the MVC pattern but in Swift this is a common practise, before I explain how structs are useful I'll