An example of the use of a finalizer (the runtime.SetFinalizer function) for a Go (golang) data structure. The documentation describes the expected signature for the function passed to SetFinalizer, but it is nice to see a running example. Tested with Go 1.1.2.

finalizer_example.go

package main

import (
        "fmt"
        "runtime"
        "time"
)

type Foo struct {
        name    string
        num     int
}

func  finalizer(f *Foo) {
        fmt.Println("a finalizer has run for ", f.name, f.num)
}

var counter int
func MakeFoo(name string) (a_foo *Foo) {
        a_foo = &Foo{name, counter}
        counter++
        runtime.SetFinalizer(a_foo, finalizer)
        return
}

func Bar() {
        f1 := MakeFoo("one")
        f2 := MakeFoo("two")

        fmt.Println("f1 is: ", f1.name)
        fmt.Println("f2 is: ", f2.name)
}

func main() {
        for i := 0; i < 3; i++ {
                Bar()
                time.Sleep(time.Second)
                runtime.GC()
        }
        fmt.Println("done.")
}

You should link play.golang.org
http://play.golang.org/p/jWhRSPNvxJ

something like:
[play](http://play.golang.org/p/jWhRSPNvxJ) with this