Pointer Receivers

A pointer receiver lets a method change the existing value or avoid copying a large receiver on each call.

Declare func (c *Counter) Increase() and call it on an addressable Counter variable. Go automatically takes the address in many ordinary method calls, so c.Increase() can work when Increase has a pointer receiver.

Method sets matter for interfaces: *Counter has methods declared with value or pointer receivers, while Counter does not have pointer-receiver methods in its method set. A method-call convenience conversion does not erase that interface rule.

Read the labels and compare the identities, types and storage relationships shown here.

This example is a complete program. Save it as main.go or paste it into the Go Playground.

Go code

package main

import "fmt"

type Counter struct{ Value int }

func (c *Counter) Increase() { c.Value++ }
func main() {
	c := Counter{Value: 5}
	c.Increase()
	c.Increase()
	fmt.Println("After calls:", c.Value)
}

Output

After calls: 7

The receiver refers to c itself. Each call increments its Value field, producing 7 after two calls.

• A pointer receiver may receive nil; accessing target fields then needs appropriate handling.
• Automatic address-taking in method calls does not make value types implement pointer-only interfaces.

Add a pointer-receiver Reset method that sets Value to zero after the increments.

Tip: Edit the example above, predict the output, and run the modified code to test your reasoning.

You have practiced Pointer Receivers in a small, self-contained program. The important habit is to predict what runs, inspect the actual output and distinguish the language rule from the particular example.

Before continuing, make sure you can explain the program to someone who has not seen it, including the line that changes its result.