value-receive and pointer-receive method

main.go

package main

import "fmt"

type Counter struct{ n int }

// ---------------------
//  ⬇ value-receiver method
// ---------------------
func (c Counter) Value() int { return c.n }

// ---------------------
//  ⬇ pointer-receiver method
// ---------------------
func (c *Counter) Inc() { c.n++ }

func main() {
	// ————————————
	// 1) Call pointer-receiver on a VALUE
	//    The compiler silently takes &v so Inc’s *Counter receiver is satisfied.
	// ————————————
	var v Counter        // value
	v.Inc()              // behind the scenes: (&v).Inc()
	fmt.Println(v.Value()) // 1

	// ————————————
	// 2) Call value-receiver on a POINTER
	//    The compiler makes a copy of *p and passes that copy to Value().
	// ————————————
	p := &Counter{3}   // pointer
	fmt.Println(p.Value()) // compiler does: (*p).Value()   → 3
	p.Inc()
	fmt.Println(p.Value()) // 4
}