Slide 1
Slide 1 text
@jrbowes
Shattered Mirror
An introduction to reflect and unsafe
Slide 2
Slide 2 text
@jrbowes
Slide 3
Slide 3 text
@jrbowes
Slide 4
Slide 4 text
@jrbowes
Slide 5
Slide 5 text
@jrbowes
Slide 6
Slide 6 text
@jrbowes
Slide 7
Slide 7 text
You are already using
reflect
@jrbowes
Slide 8
Slide 8 text
import “encoding/json"
@jrbowes
Slide 9
Slide 9 text
import “encoding/json"
func Marshal(v interface{}) ([]byte, error)
func Unmarshal(data []byte, v interface{}) error
@jrbowes
Slide 10
Slide 10 text
type Response struct {
Code int `json:"code"`
Message string `json:"message"`
}
@jrbowes
Slide 11
Slide 11 text
You are already using
reflect
@jrbowes
Slide 12
Slide 12 text
You are already using
reflect and unsafe
@jrbowes
Slide 13
Slide 13 text
package main
func main() {
}
@jrbowes
Slide 14
Slide 14 text
$> go list -f '{{.Deps}}'
@jrbowes
Slide 15
Slide 15 text
$> go list -f '{{.Deps}}'
[internal/bytealg internal/cpu runtime runtime/
internal/atomic runtime/internal/sys unsafe]
@jrbowes
Slide 16
Slide 16 text
$> go list -f '{{.Deps}}'
[internal/bytealg internal/cpu runtime runtime/
internal/atomic runtime/internal/sys unsafe]
@jrbowes
Slide 17
Slide 17 text
It starts and ends with types
@jrbowes
Slide 18
Slide 18 text
file, err := os.Open("data.txt")
@jrbowes
Slide 19
Slide 19 text
file, err := os.Open("data.txt")
@jrbowes
Slide 20
Slide 20 text
file, err := os.Open("data.txt")
var rs io.ReadSeeker = file
@jrbowes
Slide 21
Slide 21 text
file, err := os.Open("data.txt")
var rs io.ReadSeeker = file
@jrbowes
Slide 22
Slide 22 text
file, err := os.Open("data.txt")
var rs io.ReadSeeker = file
@jrbowes
w := rs.(io.Writer)
Slide 23
Slide 23 text
file, err := os.Open("data.txt")
var rs io.ReadSeeker = file
@jrbowes
w := rs.(io.Writer)
"
Slide 24
Slide 24 text
file, err := os.Open("data.txt")
var rs io.ReadSeeker = file
@jrbowes
w := rs.(io.Writer)
var r io.Reader = w.(io.ReadWriter)
"
Slide 25
Slide 25 text
file, err := os.Open("data.txt")
var rs io.ReadSeeker = file
@jrbowes
w := rs.(io.Writer)
var r io.Reader = w.(io.ReadWriter)
"
"
Slide 26
Slide 26 text
@jrbowes
os.Open("data.txt")
Slide 27
Slide 27 text
@jrbowes
os.Open("data.txt")
type File struct {}
Slide 28
Slide 28 text
@jrbowes
os.Open("data.txt")
type File struct {}
type Writer interface {}
Slide 29
Slide 29 text
The Go runtime needs your
type information
@jrbowes
Slide 30
Slide 30 text
The Go runtime needs your
type information …mostly
@jrbowes
Slide 31
Slide 31 text
reflect
@jrbowes
Slide 32
Slide 32 text
func ValueOf(i interface{}) Value
func TypeOf(i interface{}) Type
@jrbowes
Slide 33
Slide 33 text
oneThing := another
@jrbowes
Slide 34
Slide 34 text
func main() {
c := make(chan bool)
go func() {
v := reflect.ValueOf(c)
b := reflect.Zero(v.Type().Elem())
v.Send(b)
v.Close()
}()
for range c {
fmt.Println("saw value”)
}
}
@jrbowes
Slide 35
Slide 35 text
func hello(msg string) { fmt.Println(msg) }
func main() {
f := reflect.ValueOf(hello)
args := []reflect.Value{
reflect.ValueOf("hi!"),
}
f.Call(args)
}
@jrbowes
Slide 36
Slide 36 text
type A struct {
Name string
Value string `rename:"val"`
}
func main() {
a := A{Name: "a name", Value: "a value"}
v := reflect.ValueOf(a)
vt := v.Type()
for i := 0; i < v.NumField(); i++ {
f := vt.Field(i)
name := f.Name
if t, ok := f.Tag.Lookup("rename"); ok {
name = t
}
fmt.Printf("%s: %s\n", name, v.Field(i))
}
}
@jrbowes
Slide 37
Slide 37 text
func main() {
st := reflect.StructOf([]reflect.StructField{{
Name: "Message",
Type: reflect.TypeOf(""),
Tag: `json:"msg"`,
}})
s := reflect.New(st)
s.Elem().FieldByName("Message").Set(reflect.ValueOf("hi!"))
i := s.Interface()
o, _ := json.Marshal(i)
fmt.Println(string(o))
}
@jrbowes
Slide 38
Slide 38 text
@jrbowes
Slide 39
Slide 39 text
@jrbowes
Slide 40
Slide 40 text
@jrbowes
reflect.ValueOf()
reflect.MakeFunc()
Slide 41
Slide 41 text
unsafe
@jrbowes
Slide 42
Slide 42 text
@jrbowes
file, err := os.Open(“data.txt”)
var rs io.ReadSeeker = file
w := rs.(io.Writer) "
var r io.Reader = w.(io.ReadWriter) "
type Writer interface {}
type File struct {}
os.Open(“data.txt")
oneThing := another
Slide 43
Slide 43 text
@jrbowes
file, err := os.Open(“data.txt”)
var rs io.ReadSeeker = file
w := rs.(io.Writer) "
var r io.Reader = w.(io.ReadWriter) "
type Writer interface {}
type File struct {}
os.Open(“data.txt")
oneThing := another
Slide 44
Slide 44 text
type A struct {
Name string
}
type B struct {
Name, Value string
}
func main() {
b := B{"a thing", "a value”}
a := (*A)(&b)
}
@jrbowes
Slide 45
Slide 45 text
type A struct {
Name string
}
type B struct {
Name, Value string
}
func main() {
b := B{"a thing", "a value"}
a := (*A)(unsafe.Pointer(&b))
}
@jrbowes
Slide 46
Slide 46 text
func Syscall(trap, a1, a2, a3 uintptr)
(r1, r2 uintptr, err syscall.Errno)
@jrbowes
Slide 47
Slide 47 text
reflect
@jrbowes
Slide 48
Slide 48 text
reflect
@jrbowes
needs unsafe
Slide 49
Slide 49 text
package unsafe
type ArbitraryType int
type Pointer *ArbitraryType
func Sizeof(x ArbitraryType) uintptr
func Offsetof(x ArbitraryType) uintptr
func Alignof(x ArbitraryType) uintptr
@jrbowes
Slide 50
Slide 50 text
@jrbowes
Slide 51
Slide 51 text
@jrbowes
Slide 52
Slide 52 text
@jrbowes
func billingState(
ctx context.Context,
billing *client.Billing,
op *Operation
) (string, error)
next, err := step()
Slide 53
Slide 53 text
@jrbowes
func billingState(
ctx context.Context,
billing *client.Billing,
op *Operation
) (string, error)
next, err := step()
Slide 54
Slide 54 text
@jrbowes
func billingState(
ctx context.Context,
billing *client.Billing,
op *Operation
) (string, error)
next, err := step()
Slide 55
Slide 55 text
@jrbowes
func billingState(
ctx context.Context,
billing *client.Billing,
op *Operation
) (string, error)
next, err := step()
Slide 56
Slide 56 text
Don’t use reflect for
runtime dependency
injection
@jrbowes
Slide 57
Slide 57 text
Keep the flow of control in
one direction
@jrbowes
Slide 58
Slide 58 text
reflect is best for reading
@jrbowes
Slide 59
Slide 59 text
reflect is good for writing
data
@jrbowes
Slide 60
Slide 60 text
Don’t use unsafe directly ;)
@jrbowes
Slide 61
Slide 61 text
FIND ME
github.com/jbowes
twitter.com/jrbowes
manifold.co
Thank you!
@jrbowes