Methods and Receivers

package main

import "fmt"

type Counter struct {
    count int
    name  string
}

// Pointer receiver — needed to mutate
func (c *Counter) Inc() {
    c.count++
}

// Value receiver — fine when you only read
func (c Counter) String() string {
    return fmt.Sprintf("%s: %d", c.name, c.count)
}

// Convention: be consistent — if any method needs pointer receiver,
// make ALL methods pointer receivers.

func main() {
    c := Counter{name: "visits"}
    c.Inc()
    c.Inc()
    c.Inc()
    fmt.Println(c)                                  // visits: 3 (uses String())

    // Pointer methods can be called on values; Go auto-addresses
    var p Counter
    p.Inc()                                          // sugar for (&p).Inc()
    fmt.Println(p)
}