Value Receivers

A value receiver receives a copy of its receiver when a method runs. This works well for small read-only values.

In func (c Counter) Next() int, the method receives a Counter value. Reassigning fields of that local receiver does not modify the original Counter value held by the caller.

Value receivers can still observe shared data inside fields such as slices or maps: copying the struct copies those field values, not necessarily their underlying storage. Prefer a consistent receiver style for a type where possible.

Follow this diagram before executing the example. Check where a value or decision changes what runs next.

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() int {
	c.Value++
	return c.Value
}
func main() {
	c := Counter{Value: 5}
	fmt.Println("Returned:", c.Increase())
	fmt.Println("Original:", c.Value)
}

Output

Returned: 6
Original: 5

The method increments only its local copy of c to 6 and returns it. The caller’s c.Value remains 5.

• Do not expect a value-receiver field assignment to update the original struct.
• A struct copy may still share map or slice storage inside its fields.

Make a value-receiver method that doubles an integer field, returns the doubled value and leaves the original unchanged.

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

You have practiced Value 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.