Class 28: Receiver Functions in Go

🔑 Key Concept: Receiver Functions

In Go, a receiver function (also called a method) is a function that is associated with a particular type (usually a struct). It allows us to add behavior to data types, like attaching functions to objects in other languages (e.g., methods in OOP).

🧠 What Is a Receiver Function?

A receiver function is defined like a normal function, but with a special receiver parameter placed between the func keyword and the function name.

func (r ReceiverType) FunctionName(params) returnType {
    // function body
}

The receiver type can be:

• A value receiver: (t Type) → receives a copy
• A pointer receiver: (t *Type) → receives a reference (can modify original)

🏗️ From the Project Code

func (todos *Todos) add(title string) {
    todo := Todo{
        Title: title,
        Completed: false,
        CompletedAt: nil,
        CreatedAt: time.Now(),
    }
    *todos = append(*todos, todo)
}

• todos *Todos is the receiver
• This method is attached to Todos (which is a custom type: []Todo)
• The *Todos pointer allows modifications to the original slice

Example usage from main.go:

todos.add("Buy milk")

🔁 Why Use Receiver Functions?

• Organize logic with the data it operates on ✅
• Achieve OOP-like behavior in Go ✅
• Maintain cleaner and modular code ✅

💡 Extra Simple Example

type User struct {
    Name string
}

// Value receiver (no change to original)
func (u User) SayHi() {
    fmt.Println("Hi, I am", u.Name)
}

// Pointer receiver (can change original)
func (u *User) ChangeName(newName string) {
    u.Name = newName
}

func main() {
    user := User{Name: "Ruhin"}
    user.SayHi() // Hi, I am Ruhin
    user.ChangeName("Mukim")
    user.SayHi() // Hi, I am Mukim
}

⚙️ Summary

📘 Visualizing It

Think of todos.add() as calling a behavior of the object:

object.method()

This pattern lets Todos have its own custom logic, like add, delete, toggle, print, etc., just like class methods in Python/Java.