decorator_pattren.go

package main

import (
	"fmt"
	"log"
	"math"
	"os"
	"sync"
	"time"
)

type Pifunc func(int) float64

func wraplogger(fun Pifunc, logger *log.Logger) Pifunc {
	return func(n int) float64 {

		fn := func(n int) (result float64) {
			defer func(t time.Time) {
				logger.Printf("took=%v, n=%v, result=%v", time.Since(t), n, result)
			}(time.Now())
			return fun(n)
		}
		return fn(n)
	}
}

func wrapcache(fun Pifunc, cache *sync.Map) Pifunc {
	return func(n int) float64 {
		fn := func(n int) float64 {
			key := fmt.Sprintf("n=%d", n)
			val, ok := cache.Load(key)
			if ok {
				return val.(float64)
			}
			r := fun(n)
			cache.Store(key, r)
			return r
		}
		return fn(n)
	}
}

func Pi(n int) float64 {
	ch := make(chan float64)
	for i := 0; i <= n; i++ {
		go func(ch chan float64, i float64) {
			ch <- 4 * math.Pow(-1, i) / (2*i + 1)
		}(ch, float64(i))
	}

	result := 0.0
	for i := 0; i <= n; i++ {
		result += <-ch
	}
	return result
}

func Divide(n int) float64 {
	return float64(n / 2)
}

func main() {
	p := wrapcache(Pi, &sync.Map{})
	g := wraplogger(p, log.New(os.Stdout, "Pi ", 1))
	g(100000)
	g(20000)
	g(100000)
	d := wrapcache(Divide, &sync.Map{})
	dw := wraplogger(d, log.New(os.Stdout, "Divide ", 1))
	dw(1000)
	dw(55555)
	dw(55555)
}