In Swift, both classes and structs are used to define custom data types, but they have significant differences in terms of their behaviour and use cases. Understanding these differences is crucial when deciding whether to use a class or a struct for a particular purpose. Here are the key distinctions between classes and structs in Swift:
Reference vs. Value Types
Class: Classes are reference types, which means when you assign an instance of a class to a new variable or pass it as an argument to a function, you are working with references to the same object in memory. Changes to one reference affect all references to the same object.
Struct: Structs are value types, which means that when you assign an instance of a struct to a new variable or pass it as an argument, a copy of the entire struct is created. Modifications to the copy do not affect the original struct, making structs safer for data manipulation.
Class: Classes support inheritance, allowing you to create subclasses that inherit properties and methods from a superclass. Inheritance is a fundamental feature of object-oriented programming.
Struct: Structs do not support inheritance. They cannot be subclassed, which means you cannot create a "child" struct that inherits from a "parent" struct.
Class: Class instances are mutable by default. You can change the properties of a class instance even if it's declared as a constant (
Struct: Struct instances are immutable by default. When you create a struct, its properties cannot be modified unless the instance is explicitly marked as
Class: Copies of class instances point to the same underlying object in memory. If one reference modifies the object, all references see the changes.
Struct: Copies of struct instances are independent of each other. Changes to one copy do not affect other copies.
Class: Classes provide an automatic memberwise initializer, but you can also create custom initializers.
Struct: Structs provide an automatic memberwise initializer, and if you want to create custom initializers, you need to explicitly implement them.
Class: Memory management is handled using reference counting. Swift manages memory automatically using ARC (Automatic Reference Counting).
Struct: Memory management is straightforward because of the value type nature. Each instance is self-contained and independent.
Class: Classes are often used for creating complex object-oriented models, managing shared resources, and building hierarchies of related objects.
Struct: Structs are typically used for simple data structures, modeling values, and when immutability is desired.
In summary, classes and structs have distinct characteristics, and your choice between them depends on the specific requirements of your project. If you need reference semantics, inheritance, or complex modeling, classes are a suitable choice. On the other hand, if you want value semantics, immutability, and lightweight data structures, structs are a better fit.