The Evolution of a Go Programmer

Junior Go programmer

package fac

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

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

    return res
}

Functional Go programmer

package fac

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

Generic Go programmer

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
}

Multithread optimized Go programmer

package fac

import "sync"

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

    wg.Add(2)

    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
}

Discovered Go patterns

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
}

Fix Go weaknesses with mature solutions

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
}

Senior Go programmer

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
}

Tribute to the Iavor Diatchki's original page "The Evolution of a Programmer".