Class

• Supports Inheritance, DeInitializers.
• Class instances are reference types. During assignment/function call, it is the reference (address) that gets copied and not the value.

Struct

• Does not support Inheritance, DeInitializers etc.
• Struct instances are value types. During assignment/function call, it is the entire object (content) that gets copied.

Note: In Swift the types String, Array, Dictionary etc are all implemented as Structs, causing them to be copied always. However Swift uses Copy On Write to avoid unnecessary copying.

Enum

• Does not support Inheritance, DeInitializers etc.
• Enum instances are value types. During assignment/function call, it is the entire object that gets copied.