# Go 程序员的演变，Rob Pike 亮了

## 初级 Go 程序员

```package fac

func Factorial(n int) int {
res := 1

for i := 1; i <= n; i++ {
res *= i
}

return res
}```

## 函数式 Go 程序员

```package fac

func Factorial(n int) int {
if n == 0 {
return 1
} else {
return Factorial(n - 1) * n
}
}```

## 泛型 Go 程序员

```package fac

func Factorial(n interface{}) interface{} {
v, valid := n.(int)
if !valid {
return 0
}

res := 1

for i := 1; i <= v; i++ {
res *= i
}

return res
}```

## 多线程优化的 Go 程序员

```package fac

import "sync"

func Factorial(n int) int {
var (
left, right = 1, 1
wg sync.WaitGroup
)

pivot := n / 2

go func() {
for i := 1; i < pivot; i++ {
left *= i
}

wg.Done()
}()

go func() {
for i := pivot; i <= n; i++ {
right *= i
}

wg.Done()
}()

wg.Wait()

return left * right
}```

## 发现型 Go 模式

```package fac

func Factorial(n int) <-chan int {
ch := make(chan int)

go func() {
prev := 1

for i := 1; i <= n; i++ {
v := prev * i

ch <- v

prev = v
}

close(ch)
}()

return ch
}```

## 使用成熟的解决方案修复 Go 缺陷

```package fac

/**
* @see https://en.wikipedia.org/wiki/Factorial
*/
type IFactorial interface {
CalculateFactorial() int
}

// FactorialImpl implements IFactorial.
var _ IFactorial = (*FactorialImpl)(nil)

/**
* Used to find factorial of the n.
*/
type FactorialImpl struct {
/**
* The n.
*/
n int
}

/**
* Constructor of the FactorialImpl.
*
* @param n the n.
*/
func NewFactorial(n int) *FactorialImpl {
return &FactorialImpl{
n: n,
}
}

/**
* Gets the n to use in factorial function.
*
* @return int.
*/
func (this *FactorialImpl) GetN() int {
return this.n
}

/**
* Sets the n to use in factorial function.
*
* @param n the n.
* @return void.
*/
func (this *FactorialImpl) SetN(n int) {
this.n = n
}

/**
* Returns factorial of the n.
*
* @todo remove "if" statement. Maybe we should use a factory or somthing?
*
* @return int.
*/
func (this *FactorialImpl) CalculateFactorial() int {
if this.n == 0 {
return 1
}

n := this.n
this.n = this.n - 1

return this.CalculateFactorial() * n
}```

## 高级 Go 程序员

```package fac

// Factorial returns n!.
func Factorial(n int) int {
res := 1

for i := 1; i <= n; i++ {
res *= i
}

return res
}```

## Rob Pike

```package fac

// Factorial returns n!.
func Factorial(n int) int {
res := 1

for i := 1; i <= n; i++ {
res *= i
}

return res
}```