Why am I getting the \'prev declared and not used\' error in my Go code?

Go - Declared Variable Name prev is Unused in Given Function Scope

In the following code snippet, the error message "prog.go:13: prev declared and not used" is displayed.

<code class="go">package main

import "fmt"

// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func() int {
    prev := 0
    curr := 1
    return func() int {
        temp := curr
        curr := curr + prev
        prev := temp
        return curr
    }
}

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

The error occurs because the variable prev is declared in the function fibonacci, but it is never used. Specifically, the line prev := temp creates a new local variable named prev. This variable is different from the prev variable declared in the outer scope. To fix the error, we need to modify the code to use the prev variable from the outer scope instead of creating a new local variable.

Here is the corrected code:

<code class="go">package main

import "fmt"

// fibonacci is a function that returns
// a function that returns an int.
func fibonacci() func() int {
    prev := 0
    curr := 1
    return func() int {
        temp := curr
        curr = curr + prev
        prev = temp
        return curr
    }
}

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

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