🧰 Go Method Functions – Define Functions on Structs with Receivers (2025 Guide)

🧲 Introduction – What Are Method Functions in Go?

In Go, method functions are functions associated with a specific type, usually a struct. Unlike regular functions, methods use a receiver to operate on an instance of a type—similar to methods in OOP languages, but simpler and more explicit.

🎯 In this section, you’ll learn:

• How to define and call methods in Go
• The difference between value and pointer receivers
• How methods compare with regular functions
• Real-world use cases with structs and interfaces

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✅ Basic Syntax – Defining a Method on a Struct

type Person struct {
    name string
}

// Method with value receiver
func (p Person) greet() {
    fmt.Println("Hello,", p.name)
}

✅ The (p Person) part is called the receiver—it tells Go that greet is a method on the Person type.

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🔁 Calling a Method

p := Person{name: "Go Dev"}
p.greet()

📤 Output:

Hello, Go Dev

✅ Looks just like calling a function on an object.

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🔃 Pointer Receiver vs Value Receiver

📥 Value Receiver (copy):

func (p Person) rename(newName string) {
    p.name = newName
}

🔧 Pointer Receiver (modifies original):

func (p *Person) rename(newName string) {
    p.name = newName
}

Example:

p := Person{name: "Alice"}
p.rename("Bob")
fmt.Println(p.name) // Output depends on receiver type

📤 Output:

• Value receiver → Alice
• Pointer receiver → Bob

✅ Use pointer receivers when you want to modify the original struct or avoid copying large structs.

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🧩 Methods vs Functions in Go

Feature	Method	Function
Requires receiver?	✅ Yes	❌ No
Syntax	func (t Type) name()	func name(t Type)
Used for	Type-specific behaviors	General-purpose logic
Works with interfaces	✅ Yes (via method sets)	❌ Only via adapter/wrappers

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📚 Example – Method with Pointer Receiver

type Account struct {
    balance float64
}

func (a *Account) Deposit(amount float64) {
    a.balance += amount
}

func (a Account) ShowBalance() {
    fmt.Printf("Current Balance: ₹%.2f\n", a.balance)
}

func main() {
    acc := Account{}
    acc.Deposit(1500)
    acc.ShowBalance()
}

📤 Output:

Current Balance: ₹1500.00

✅ Deposit modifies the actual struct using a pointer receiver.

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🧠 Method Sets – Interface Compatibility

Only types with the required method set can implement interfaces:

type Speaker interface {
    Speak()
}

type Dog struct{}

func (d Dog) Speak() {
    fmt.Println("Woof!")
}

func saySomething(s Speaker) {
    s.Speak()
}

saySomething(Dog{}) // ✅ Dog implements Speaker

✅ Method functions enable Go’s interface system, even without classes or inheritance.

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📌 Summary – Recap & Next Steps

Method functions in Go allow you to associate behavior with custom types. They’re foundational for interfaces, clean code organization, and object-like patterns in Go.

🔍 Key Takeaways:

• Method functions use receivers to bind behavior to a type
• Use value receivers for read-only logic, pointer receivers to mutate
• Methods help implement interfaces
• More explicit than traditional OOP, but just as powerful

⚙️ Next: Learn about Go Variadic Functions to handle dynamic-length parameters in your functions and methods.

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❓ FAQs – Go Method Functions

❓ What is a method in Go?
✅ A function with a receiver that’s attached to a type, like a struct.

❓ Can I define methods on non-struct types?
✅ Yes, but only on named types (not built-in types like int directly).

❓ When should I use pointer receivers?
✅ Use them when your method needs to modify the receiver’s state or avoid copying large structs.

❓ Can methods be used to implement interfaces?
✅ Yes. Types implement interfaces implicitly by defining the required methods.

❓ What happens if I define both pointer and value receiver methods?
✅ Go automatically converts between value and pointer when calling the method—based on need.

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