Methods for fetching structure fields in Go (golang)

gistfile1.go

package main

import "log"
import "time"
import "reflect"

// suggested via http://stackoverflow.com/a/8363629/87207
func trace(s string) (string, time.Time) {
    log.Println("START:", s)
    return s, time.Now()
}

// suggested via http://stackoverflow.com/a/8363629/87207
func un(s string, startTime time.Time) {
    endTime := time.Now()
    log.Println("  END:", s, "ElapsedTime in seconds:", endTime.Sub(startTime))
}

type S struct {
	A int
	B int
	C int
	D int
	E int
	F int
	G int
	H int
	X int
	Y int
}

type Getter func(*S, string) int

// get a field by static offset
func getField(s *S, _ string) int {
	return s.X
}

// dynamically lookup a field
// 40x slower than getField()
func reflectField(s *S, field string) int {
	r := reflect.ValueOf(s)
	f := reflect.Indirect(r).FieldByName(field)
	return int(f.Int())
}

// create a function that knows what slot to fetch given a name.
// 10x slower than getField()
func makeFieldGetter(v reflect.Value, field string) Getter {
  t := v.Type()
  for i := 0; i < v.NumField(); i++ {
    if t.Field(i).Name == field {
      return func(s *S, _ string) int {
        av := reflect.ValueOf(s).Elem()
        i, _ := av.Field(i).Interface().(int)
        return i
      }
    }
  }
  return nil
}

func testMethod(name string, s *S, f Getter) {
  defer un(trace(name))
  for i := 0; i < 10 * 1000 * 1000; i++ {
    x := f(s, "X")
    x = x
  }
}

func main() {
  s := S{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
  testMethod("direct", &s, getField)
  testMethod("getter", &s, makeFieldGetter(reflect.ValueOf(&s).Elem(), "X"))
  testMethod("reflect", &s, reflectField)
}

results

» go build && ./reflector                                       
2015/06/09 22:51:07 START: direct
2015/06/09 22:51:08   END: direct ElapsedTime in seconds: 50.241986ms
2015/06/09 22:51:08 START: getter
2015/06/09 22:51:08   END: getter ElapsedTime in seconds: 464.712541ms
2015/06/09 22:51:08 START: reflect
2015/06/09 22:51:10   END: reflect ElapsedTime in seconds: 2.416859844s