awesome-patterns/profiling/profile.go

package profile

import (
	"log"
	"math/big"
	"time"
)

func Duration(invocation time.Time, name string) {
	elapsed := time.Since(invocation)

	log.Printf("%s lasted %s", name, elapsed)
}

func BigIntFactorial(x big.Int) *big.Int {
	// Arguments to a defer statement is immediately evaluated and stored.
	// The deferred function receives the pre-evaluated values when its invoked.
	defer Duration(time.Now(), "IntFactorial")

	y := big.NewInt(1)
	for one := big.NewInt(1); x.Sign() > 0; x.Sub(&x, one) {
		y.Mul(y, &x)
	}

	return x.Set(y)
}