Classes vs. Structs in Swift: Which Should You Use?

Definition and Syntax 

In Swift, both structs and classes can be used to define custom data types. 

The syntax for defining a struct is as follows:

struct MyStruct {
  // properties and methods
}

The syntax for defining a class is similar:

class MyClass {
  // properties and methods
}

Reference vs Value Type

One of the most important differences between structs and classes is how they are handled in memory. Structs are value types, which means that when you create an instance of a struct, it is copied. This means that each instance of a struct has its own copy of the data, and modifications to one instance do not affect other instances.

On the other hand, classes are reference types. This means that when you create an instance of a class, a reference to that instance is created. If you create multiple variables that refer to the same instance of a class, they all refer to the same object in memory. Modifying one variable will affect all variables that refer to the same object.

Inheritance

Another key difference between structs and classes is that classes can inherit from other classes, while structs cannot. This means that classes can be used to create class hierarchies and to reuse code.

For example, you can define a base class with common properties and methods, and then create subclasses that inherit from the base class and add their own properties and methods. This can make it easier to manage code and to make changes to shared functionality.

Mutability

Structs in Swift are by default immutable. This means that once you create an instance of a struct, you cannot modify its properties. If you want to modify a property of a struct, you need to create a new instance of the struct with the updated property value.

On the other hand, classes in Swift are mutable by default. This means that you can modify the properties of a class instance after it has been created.

Advantages and Disadvantages

When choosing between a struct and a class, it's important to consider the advantages and disadvantages of each.

Advantages of using a struct:

• Structs are value types, which means that they are copied when passed around in code. This can make it easier to reason about code and to avoid unexpected side effects.
• Structs are immutable by default, which can make them safer to use in concurrent code.
• Structs can be used to create simple data models that don't require inheritance or other advanced features.

Disadvantages of using a struct:

• Structs cannot inherit from other structs, which can make it harder to reuse code.
• Structs can be less efficient than classes for large data models, since each instance is copied when passed around in code.

Advantages of using a class:

• Classes can inherit from other classes, which can make it easier to reuse code and to create complex class hierarchies.
• Classes can be more efficient than structs for large data models, since only a reference to the instance is passed around in code.
• Classes can be used to create objects that require mutability, such as UI elements or network connections.

Disadvantages of using a class:

• Classes are reference types, which can make it harder to reason about code and to avoid unexpected side effects.
• Classes can be more complex than structs, which can make them harder to maintain and debug.

Appropriate Use

In general, you should use a struct when:

• You are creating a simple data model with a small number of properties.
• You don't need inheritance or other advanced features.
• You want to create an immutable object.

You should use a class when:

• You need to create objects that require mutability, such as UI elements or network connections.
• You need to create complex object hierarchies that require inheritance and polymorphism.
• You are working with large data models, since classes can be more efficient than structs for passing around large objects.

In general, if you need to create objects that require mutability or complex object hierarchies, you should use a class. Classes are also a good choice for working with large data models, since they can be more efficient than structs for passing around large objects. However, if you are creating a simple data model with a small number of properties and don't need inheritance or other advanced features, you should use a struct instead.