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Huseyn
Huseyn

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Functions vs Methods in Go

#go #backend

🧩 1. Functions
A function in Go is a block of code that performs a task and can optionally return values. It's not associated with any type.

// syntex
func functionName(params) returnType {
    // logic
}
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// example
func add(a int, b int) int {
    return a + b
}

result := add(2, 3) // result = 5
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  • Standalone
  • Can be called anywhere in the same package
  • No receiver

🧱 2. Methods
A method is a function with a receiver — it is associated with a type (usually a struct).

// syntex
func (r ReceiverType) methodName(params) returnType {
    // logic
}
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The receiver can be a value or a pointer.

// example
type User struct {
    name string
}

func (u User) greet() {
    fmt.Println("Hello,", u.name)
}
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u := User{name: "Alice"}
u.greet() // Output: Hello, Alice
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📌 Differences at a Glance

Feature Function Method
Associated With None A type (struct, alias, etc.)
Syntax func name() func (r Type) name()
Call name() variable.name()
Use Case General purpose operations Behaviors/actions tied to specific types
OOP Concept Not applicable Like instance methods in OOP

🧠 Receiver Types: Value vs Pointer
📦 Value Receiver ((u User))

  • Method gets a copy.
  • Cannot modify original data. 
func (u User) setName(name string) {
    u.name = name // won't affect original
}
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🧷 Pointer Receiver ((u *User))

  • Method gets a reference.
  • Can modify the original. 
func (u *User) setName(name string) {
    u.name = name // modifies original
}
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Go allows calling pointer-receiver methods on values and vice versa (automatic conversion).

// Example : Function vs Method
type Rectangle struct {
    width, height float64
}

// Function
func area(r Rectangle) float64 {
    return r.width * r.height
}

// Method
func (r Rectangle) Area() float64 {
    return r.width * r.height
}
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Both do the same job, but the method feels more object-oriented.

🧪 When to Use What?

Use Case Choose...
Independent utility logic Function
Logic tied to a specific type Method
Want to modify a struct Pointer method
Behavior abstraction Method

Methods on Non-Struct Types
Go allows defining methods on any named type, even primitives.

type MyInt int

func (m MyInt) Double() int {
    return int(m * 2)
}

var x MyInt = 5
fmt.Println(x.Double()) // 10
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Summary

  • Functions = general-purpose, independent code blocks.
  • Methods = functions bound to a type, useful for behavior and encapsulation.
  • Use pointer receivers to modify values or avoid copying.
  • Methods make code more modular, readable, and idiomatic in Go.

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