Why Does Go Throw \'prev declared and not used\' Error Despite Variable Initialization?

Go - Error: "prev declared and not used", Despite Variable Initialization

In Go, encountering the error "prev declared and not used" when variables appear initialized can be puzzling. Let's examine a specific case:

<code class="go">package main

import "fmt"

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 issue lies in the inner anonymous function within fibonacci(). The code declares a variable prev, which is shadowed by the subsequent := assignment. This creates a new local variable that is not used, triggering the "prev declared and not used" error.

Resolution:

To solve this problem, modify the := assignment to =. This assigns the value of temp to the inherited prev variable:

<code class="go">prev = temp</code>

Similarly, the next line should be:

<code class="go">curr = curr + prev</code>

This ensures that prev is properly used and the error is resolved.

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