Enums - Structs - Classes in Swift

Enums:

• An enumeration defines a common type for a group of related values.
• Enums are value types that have a set of cases, where each case can have different associated values. 
• Each value of an enum type represents a single case as defined by the enum. 
• They can’t have any stored properties.(let, var)

Syntax:
enum SomeEnumeration {
  // enumeration definition goes here
}

Structs:

Common features for Classes and Structs:

• Define properties to store values 
• Define methods to provide functionality 
• Define subscripts to provide access to their values using subscript syntax 
• Define initializers to set up their initial state 
• Be extended to expand their functionality beyond a default implementation 
• Conform to protocols to provide standard functionality of a certain kind

Extra benefits of classes:

• Inheritance enables one class to inherit the characteristics of another. 
• Type casting enables you to check and interpret the type of a class instance at runtime. 
• Deinitializers enable an instance of a class to free up any resources it has assigned. 
• Reference counting allows more than one reference to a class instance.

Syntax:
struct SomeStructure { 
   // structure definition goes here
}

Classes:

Unlike value types, reference types are not copied when they are assigned to a variable or constant, or when they are passed to a function. Rather than a copy, a reference to the same existing instance is used instead.
Syntax:
class SomeClass {  
  // class definition goes here
}