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())
	}
}

I used growing slice as well but clearly there are better answers here

package main

import "fmt"

// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func() int {
    seq := 0
    var f []int
    
    return func() int {
        switch seq {
            case 0,1:
            f = append(f, seq)
            default:
            f = append(f, f[seq-2]+f[seq-1])
        }
        seq++
        return f[len(f)-1]
    }
}

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

func fibonacci() func() int {
	prev := -1
	now := 1

	return func() int {
		now +=  prev
		prev = now - prev
		return now
	}
}

`package main

import "fmt"

// fibonacci is a function that returns
// a function that returns an int

func fibonacci() func(int) int {
sum := 0
sum1 := 0
sum2 := 1
return func(x int) int {
if x == 0 {
return sum1
} else if x == 1 {
return sum2
} else {
sum = sum1 + sum2
sum1 = sum2
sum2 = sum
return sum
}
}
}

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

Feels succinct:

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

Wired & fun solution

---

package main

import "fmt"

func fib() func(int) int {
a := 0
b := 1
return func(count int) int {
for ; count > 0; count-- {
a, b = b, a+b
}
return a
}
}

func main () {
fibCalc := fib()
fmt.Println(fibCalc(10))
}

func fibonacci() func() int {
    num, back, n := 0, 1, 0
	  return func () int {
		  if n++; n == 1 {
			  return 0
		  }
		  num, back = num+back, num
		  return num
	  }
}

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())
	}
}

package main

import "fmt"


// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func(int) int {
	return func(x int) int {
		 
		switch x {
		case 0:
			return 0
		case 1:
			return 1
		default:
			return fibonacci()(x-1) + fibonacci()(x-2)
		}
	}

}


func main() {

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

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