Multiple Inheritance

Definition

Multiple inheritance allows a child class to inherit from more than one parent class. This is more powerful but also more complex.

⚠️ Not supported in many languages. JavaScript, TypeScript, Java, and C# do NOT support multiple inheritance with classes. Python and C++ do.

Characteristics

Aspect	Description
Parents	Two or more parent classes
Children	One child inherits from multiple parents
Complexity	High — especially the diamond problem
Support	Python, C++ (not Java, JS, C#)

The Diamond Problem

The main issue with multiple inheritance is the diamond problem:

graph TD
    A[Class A] --> B[Class B]
    A --> C[Class C]
    B --> D[Class D]
    C --> D
    D --> Problem["❌ Diamond Problem<br/>Which implementation of method()<br/>from B or C does D inherit?"]

Python Example (with MRO)

Python uses Method Resolution Order (MRO) — C3 linearization — to solve the diamond problem.

class A:
    def method(self):
        return "A"

class B(A):
    def method(self):
        return "B"

class C(A):
    def method(self):
        return "C"

class D(B, C):
    pass

d = D()
print(d.method())  # "B" — follows MRO: D → B → C → A
print(D.__mro__)   # Shows the MRO chain

Interfaces as Alternatives

In languages without multiple inheritance, use interfaces to achieve similar capability:

interface Swimmable {
  swim(): void;
}

interface Flyable {
  fly(): void;
}

class Duck implements Swimmable, Flyable {
  swim() { console.log("Swimming"); }
  fly() { console.log("Flying"); }
}

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