go_pointer_and_value_receivers.md

Golang Pointer and Value receivers

• Associating Methods with Types:
  • The receiver allows you to associate a method with a specific type, either a struct or a named type. This makes the function a method that can be called on instances of that type.
  • For example, with func (r *ServiceAccountResource) Configure(...), Configure is a method that can be called on any instance of ServiceAccountResource.
• Accessing Instance Data:
  • The receiver gives you access to the fields and methods of the instance it is called on, much like self in Python.
  • If ServiceAccountResource has fields, within the Configure method, you can access them using r.
• Pointer vs Value Receivers:
  • A receiver can be either a value or a pointer. This choice has significant implications:
  • Value Receiver: A copy of the type is passed to the method. Modifications to the receiver inside the method do not affect the original instance.
  • Pointer Receiver: A pointer to the type is passed to the method. Modifications to the receiver inside the method will affect the original instance.
  • For example, func (r ServiceAccountResource) Configure(...) would use a value receiver, while func (r *ServiceAccountResource) Configure(...) uses a pointer receiver. The latter is more common when the method needs to modify the instance or avoid copying large structs.
• Method Sets:
  • The receiver type determines the method set, which is the set of methods that are available to a type. Methods with pointer receivers belong to the method set of both the pointer and the value type, whereas methods with value receivers belong only to the value type.

Example

package main

import "fmt"

// Define a struct type
type ServiceAccountResource struct {
    client string
}

// Define a method with a pointer receiver
func (r *ServiceAccountResource) Configure(client string) {
    r.client = client // This modifies the original instance
}

// Define a method with a value receiver
func (r ServiceAccountResource) Display() {
    fmt.Println("Client:", r.client) // This only accesses a copy of the instance
}

func main() {
    var res ServiceAccountResource
    
    res.Configure("ExampleClient")
    res.Display() // Output: Client: ExampleClient

    copy := res
    copy.Configure("NewClient")
    res.Display() // Output: Client: ExampleClient (original instance remains unchanged)
}