unsafe package

//  - bytes_and_strings.go - 
package main

import (
	"unsafe"

	"github.com/davecgh/go-spew/spew"
)

func main() {
	s, b := "string", []byte("string")

	spew.Dump(*(*[]byte)(unsafe.Pointer(&s)))
	spew.Dump(*(*string)(unsafe.Pointer(&b)))
}

//  - main.go - 
package main

import (
	"fmt"
	"unsafe"
)

type Programmer struct {
	name     string
	language string
}

func main() {
	p := Programmer{"stefno", "go"}
	fmt.Println(p)

	name := (*string)(unsafe.Pointer(&p))
	*name = "qcrao"

	lang := (*string)(unsafe.Pointer(uintptr(unsafe.Pointer(&p)) + unsafe.Offsetof(p.language)))
	*lang = "Golang"

	fmt.Println(p)
}

//  - slice.go - 
package main

import (
	"reflect"
	"unsafe"

	"github.com/davecgh/go-spew/spew"
)

func main() {
	/// slices...
	data := []int{1, 2, 3, 4, 5}
	var out []byte
	in := (*reflect.SliceHeader)(unsafe.Pointer(&data))
	outHeader := (*reflect.SliceHeader)(unsafe.Pointer(&out))
	outHeader.Data = in.Data
	outHeader.Len = in.Len * int(unsafe.Sizeof(&data[0]))
	outHeader.Cap = in.Cap * int(unsafe.Sizeof(&data[0]))

	// out is altered!

	spew.Dump(out)
}

//  - struct.go - 
package main

import (
	"unsafe"

	"github.com/davecgh/go-spew/spew"
)

// packing struct to butes

func main() {
	// structs...
	type Struct struct {
		Src     int32
		Dst     int32
		SrcPort uint16
		DstPort uint16
	}

	var struct_value Struct = Struct{1, 2, 3, 4}
	const size = int(unsafe.Sizeof(Struct{}))
	var asByteSlice []byte = (*(*[size]byte)(unsafe.Pointer(&struct_value)))[:]

	spew.Dump(asByteSlice)
}