Methods

Go supports methods defined on struct types.

package main

import "fmt"

type rect struct {
    width, height int
}

// This area method has a receiver type of *rect.
func (r *rect) area() int {
    return r.width * r.height
}

// Methods can be defined for either pointer or value receiver types.
// Here’s an example of a value receiver.
func (r rect) perim() int {
    return 2*r.width + 2*r.height
}

func main() {
    r := rect{width: 10, height: 5}

    // Here we call the 2 methods defined for our struct.
    fmt.Println("area: ", r.area())
    fmt.Println("perim:", r.perim())

    // Go automatically handles conversion between values and pointers for method calls.
    // You may want to use a pointer receiver type to avoid
    // copying on method calls or to allow the method to mutate the receiving struct.
    rp := &r
    fmt.Println("area: ", rp.area())
    fmt.Println("perim:", rp.perim())
}

$ go run methods.go
area:  50
perim: 30
area:  50
perim: 30

Next we’ll look at Go’s mechanism for grouping and naming related sets of methods: interfaces.