Pointer Tagging in Go

gistfile1.go

package main

import (
	"fmt"
	"github.com/chewxy/gogogadget"
	"unsafe"
)

func main() {
	var x int64 = 1234

	// xPointer is of the *int64 type, meaning it points to
	// an object in memory that is a int64
	var xPointer *int64 = &x

	// converts xPointer into an unsafe.Pointer, which is then converted
	// into uintptr, which is then converted into uint
	var xPointerUint uint = uint(uintptr(unsafe.Pointer(xPointer)))

	// Prints the binary representation
	fmt.Println(gogogadget.BinaryRepresentation(xPointerUint))
	
	// makes xPointerUint into a tagged pointer
	// this destroys any capability of xPointerUint's
	// capability to be used as a pointer
	TagPointer(&xPointerUint, uint(5))

	fmt.Println(gogogadget.BinaryRepresentation(xPointerUint))

	// get a new uint for rtnPointer and tag
	rtnPointer := ReturnPointer(&xPointerUint)
	tag := ReturnTag(&xPointerUint)

	// convert rtnPointer into a *int64, then indirect to get the RestoredValue
	RestoredValue := *(*int64)(unsafe.Pointer(uintptr(rtnPointer)))
	fmt.Println(RestoredValue)
	fmt.Println(tag)
}

func TagPointer(ptr *uint, i uint) {
	x := (*ptr | i)
	*ptr = x
}

func ReturnPointer(ptr *uint) uint {
	return (*ptr &^ uint(7))
}

func ReturnTag(ptr *uint) uint {
	return *ptr & uint(7)
}