How Can I Effectively Implement Methods on Go Interfaces Without Multiple Inheritance?

Why Use Interfaces in Go?

Interfaces in Go enable polymorphism, allowing you to create generic types that can work with any type implementing those interfaces. However, unlike languages like Java or C , Go does not support multiple inheritance. This raises the question of how to achieve certain design patterns, such as using a type that "should implement" two interfaces, without inheritance.

Your Use Case

To hide your struct type and represent it as an interface:

type Card interface {
    GetFace() string
    GetSuit() string
}

You also want to define a String() method for your Card interface, but this presents a challenge as you cannot pass an interface to the String() method's implementation.

Alternative Approach

Instead of using the anti-pattern of hiding your struct and exporting only the interface, consider the following approach:

Export a Pointer to the Struct

Hide your struct fields to prevent external modification, but export a pointer to it:

type Card struct {
    // ... struct fields here
}

func NewCard(...) *Card {
    // ...
}

Implement String() for the Pointer Type

Define a String() method for the pointer to your Card struct:

func (c *Card) String() string {
    // ...
}

This approach allows you to:

• Hide struct details while exposing the interface.
• Keep the interface decoupled from specific implementations.
• Provide a String() representation for clients using the interface.

Conclusion

While the "interface hiding" pattern may seem appealing, it can lead to poor encapsulation, hurt documentation, and introduce unnecessary complexity. The recommended approach of exporting a pointer to the struct and implementing the String() method on the pointer type provides a cleaner and more effective solution.

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