Why Does Go Give the Error \'err declared and not used\'?

Variable Unused in Go: Explained

The error message "err declared and not used" is a common compilation issue in Go. It arises when a variable is declared but not utilized within the scope. To comprehend this issue, let's delve into the given code snippet:

package main

import (
    "fmt"
)

func main() {
    var (
        err error
        dto = make(map[string]interface{})
    )

    dto[`thing`], err = getThings()
    fmt.Println(dto[`thing`])
}

func getThings() (string, error) {
    return `the thing`, nil
}

In this code, the err variable is declared but not used to handle any error. As a result, the compiler issues the "declared and not used" error. It's not a scope or shadowing issue, as the err variable is properly declared within the main function.

According to the Go FAQ, the presence of an unused variable can indicate a potential bug. However, unused imports only slow down compilation. Declared variables must be used, and in this case, err is not assigned or utilized for error handling.

One way to address this is by bypassing the error checking:

var _ = err

Alternatively, you could use err for actual error handling:

if err != nil {
    fmt.Println(err.Error())
    return
}

However, it's generally advisable to utilize err for error checking rather than simply assigning it.

In conclusion, the error "err declared and not used" arises when a variable is declared but not utilized within its scope. This can be resolved by either bypassing the error checking or using the variable for its intended purpose, such as error handling.

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