An answer of the exercise: Fibonacci closure on a tour of Go

fibonacci_closure.go

package main

import "fmt"

// Very naive answer.
// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func() int {
	n := 0
	a := 0
	b := 1
	c := a + b
	return func() int {
		var ret int
		switch {
		case n == 0:
			n++
			ret = 0
		case n == 1:
			n++
			ret = 1
		default:
			ret = c
			a = b
			b = c
			c = a + b
		}
		return ret
	}
}

func main() {
	f := fibonacci()
	for i := 0; i < 10; i++ {
		fmt.Println(f())
	}
}

func fibonacci() func() int {
	first := -1
	second := 1
	return func() int {
		first, second = second, first + second
		return second
	}
}

func fibonacci() func() int {
	i := -1
	var fib func(i int) int
	
	fib = func(x int) int {
		switch x {
			case 0:
				return 0
			case 1:
				return 1
			default:
				return fib(x-1) + fib(x-2)
		}
	}
	
	fib2 := func() int {
		i++
		return fib(i)
	}
	return fib2
}

func fibonacci() func() int {
	a, b := 0, 1
	fib := func() int {
		var result int
		if a == 0 {
			result = 0
		} else {
			result = b
		}
		a, b = b, a+b
		return result
	}
	return fib
}

func fibonacci() func() int {
	array := [2]int {-1, 1}
	return func() int{
		res := array[0] + array[1]
		array[0] = array[1]
		array[1] = res
		return res
	}
}

package main

import "fmt"

// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func() int {
	
	first, second := 0, 1
	
	return (func () int {
		first, second = second, first + second
		return second
		
	})

}

func main() {
	f := fibonacci()
	for i := 0; i < 10; i++ {
		fmt.Println(f())
	}
}

anybody can explain for me about this line "first, second = second, first + second" ? please, i don't understand

func fibonacci() func() int {
	a,b,c := 0, 0, 1
	return func() int {
		a = b
		b, c = c, b+c
		return a
	}
}

@QuanTT0110
similar to writing:

first = second
second = first + second

package main

import "fmt"

// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func() int {
	
	first, second := 0, 1
	
	return (func () int {
		first, second = second, first + second
		return second
		
	})

}

func main() {
	f := fibonacci()
	for i := 0; i < 10; i++ {
		fmt.Println(f())
	}
}

anybody can explain for me about this line "first, second = second, first + second" ? please, i don't understand

I think you need to create a copy. Remember you are using a accumulating reference in first and second. Also think about your logic one more time

I solved this using a defer function:

package main

import "fmt"

// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func() int {
	var a, b int = 0, 1

	return func() int {
		update_fn := func() {
			a, b = b, b+a
		}
		defer update_fn()
		return a
	}
}

func main() {
	f := fibonacci()
	for i := 0; i < 10; i++ {
		fmt.Println(f())
	}
}