Why inheritance is class-only in Swift - Visual Breakdown

Concept Flow - Why inheritance is class-only in Swift

Define class A

↓

Define class B inheriting A

↓

Create instance of B

↓

Access properties/methods from A and B

↓

Attempt inheritance with struct/enum

↓

Compilation error: inheritance not allowed

↓

Reason: structs/enums are value types, classes are reference types

↓

Conclusion: inheritance only for classes

Inheritance works only with classes because classes are reference types that support shared behavior, while structs and enums are value types that do not support inheritance.

Execution Sample

Swift

class Animal {
    func sound() -> String { "Some sound" }
}

class Dog: Animal {
    override func sound() -> String { "Bark" }
}

Defines a base class Animal and a subclass Dog that inherits and overrides a method.

Execution Table

Step	Action	Evaluation	Result
1	Define class Animal	Animal class created	Animal class ready
2	Define class Dog inheriting Animal	Dog inherits Animal	Dog class ready with Animal's methods
3	Create instance dog of Dog	dog is Dog instance	dog can call sound()
4	Call dog.sound()	Dog's sound() overrides Animal's	"Bark" returned
5	Try inheritance with struct	struct cannot inherit	Compilation error
6	Try inheritance with enum	enum cannot inherit	Compilation error

💡 Inheritance stops at structs/enums because they are value types and do not support inheritance.

Variable Tracker

Variable	Start	After Step 3	After Step 4	Final
dog	nil	Dog instance created	dog.sound() returns "Bark"	dog remains Dog instance

Key Moments - 2 Insights

Why can't structs or enums inherit from other types?

Structs and enums are value types that copy data, so inheritance (which relies on shared references) is not supported, as shown in execution_table steps 5 and 6.

Why does Dog override Animal's sound() method?

Because Dog inherits from Animal (a class), it can override methods to provide specific behavior, as seen in execution_table step 4.

Visual Quiz - 3 Questions

Look at the execution table, what does dog.sound() return at step 4?

A Compilation error

B "Some sound"

C "Bark"

D nil

💡 Hint

Check execution_table row with Step 4 where dog.sound() is called.

At which step does the code show inheritance is not allowed for structs?

A Step 3

B Step 5

C Step 2

D Step 6

💡 Hint

Look at execution_table rows for struct inheritance attempts.

If Dog was a struct instead of a class, what would happen?

A It would cause a compilation error

B It would inherit Animal successfully

C It would override methods like a class

D It would behave like a class instance

💡 Hint

Refer to execution_table steps 5 and 6 about inheritance restrictions.

Concept Snapshot

Inheritance in Swift works only with classes.
Classes are reference types allowing shared behavior.
Structs and enums are value types and cannot inherit.
Trying inheritance with structs/enums causes errors.
Use classes when you need inheritance.

Full Transcript

In Swift, inheritance is allowed only for classes because classes are reference types that share behavior through a common identity. Structs and enums are value types that copy data and do not support inheritance. The code example shows a base class Animal and a subclass Dog that overrides a method. When trying to inherit with structs or enums, the compiler gives an error. This is because inheritance relies on shared references, which value types do not have. Therefore, inheritance is class-only in Swift.