Difference Between Struct and Interface in Golang

1. Introduction

In Golang, structs and interfaces are two fundamental concepts used for different purposes in structuring programs. A struct (short for structure) is a composite data type that groups together variables (fields) under a single name, providing a way to handle related data. An interface, on the other hand, is a type that specifies a method set, defining behavior but not implementation. It represents a set of method signatures and is used to express a contract or a capability.

2. Key Points

1. Composition: Structs are about data composition, and interfaces are about method definition.

2. Implementation: Structs can have concrete data and methods, interfaces only define method signatures.

3. Usage: Structs are used to model concrete things, and interfaces to define capabilities or behaviors.

4. Polymorphism: Interfaces enable polymorphism, allowing different structs to be treated uniformly based on shared behavior.

3. Differences

Characteristic	Struct	Interface
Composition	Data composition	Method definition
Implementation	Concrete data and methods	Method signatures only
Usage	Model concrete things	Define capabilities/behaviors
Polymorphism	Not directly related	Enables polymorphism

4. Example

// Example of a Struct
type Car struct {
    Make  string
    Model string
}

// Example of an Interface
type Vehicle interface {
    Drive() string
}

// Implementing an Interface
func (c Car) Drive() string {
    return "Driving a " + c.Make + " " + c.Model
}

Output:

Struct Output:
Car{Make: "Toyota", Model: "Corolla"}
Interface Output:
Implementation of Drive() method for Car

Explanation:

1. The Car struct is a concrete representation of a car with Make and Model as its properties.

2. The Vehicle interface defines a behavior (Drive), but not how it's implemented. The Car struct then implements this behavior.

5. When to use?

- Use structs when you need to group data and create concrete objects with specific properties.

- Use interfaces to define behaviors and capabilities, and when you need polymorphic behavior, allowing different structs to be treated uniformly based on shared behavior.