Golang complaining about unused variable inside for-loop-CodePudding

I have an unused variable inside a for-loop in golang.

I'm actually using it outside the for loop.

Goland keeps complaining about the unused variable.

How do I fix this?

var backoffSchedule = []time.Duration{
    1 * time.Second,
    3 * time.Second,
    10 * time.Second,
}
var response *http.Response

for _, backoff := range backoffSchedule {
    response, err := client.Do(request)
    if err == nil {
        break
    }
    fmt.Printf(os.Stderr, "Request error: %s", err)
    fmt.Printf(os.Stderr, "Retrying in %s", backoff)
    time.Sleep(backoff)

}

if err != nil {
    fmt.Printf("CRITICAL: API request failed: %s", err)
    os.Exit(2)
}

if response.StatusCode <= 199 || response.StatusCode >= 300 {
    // Non-successful response, alert
    fmt.Printf("CRITICAL: APIv request returned not ok: %s", response.Status)
    os.Exit(2)

It's also complaining about the unreferenced variable err. How do I make them available inside the function.

CodePudding user response：

One way to make the error disappear would be to declare an err variable outside the loop:

var err error

That way, you can assign existing variables (rather than declare new variables) inside the loop

for _, backoff := range backoffSchedule {
    response, err = client.Do(request)
                 ^^^

Make sure this is what you want though, as response will be, outside the loop, the last value assigned in the loop.

CodePudding user response：

You have two variables named response, one inside the loop and another outside the loop.

Here is an example that demonstrates the same issue.

package main

import (
    "fmt"
)

func foo() (int, error) {
    return 10, nil
}

func main() {
    someValue := 5
    
    if (someValue == 5) {
        someValue, err := foo()
        if (err == nil) {
            fmt.Println("Inside if scope:", someValue)
        }
    }
    
    fmt.Print("Outside if scope:", someValue)
}

The issue here is that you are using :=, which by default creates a new variable.

If you declare err outside of the scope and use = your code will work.

package main

import (
    "fmt"
)

func foo() (int, error) {
    return 10, nil
}

func main() {
    someValue := 5
    var err error
    
    if (someValue == 5) {
        someValue, err = foo()
        if (err == nil) {
            fmt.Println("Inside if scope:", someValue)
        }
    }
    
    fmt.Print("Outside if scope:", someValue)
}

Another note to how go behaves is that if you are in the same scope as an already existing variable, it works differently.

package main

import (
    "fmt"
)

func foo() (int, error) {
    return 10, nil
}

func main() {
    someValue := 5
    
    fmt.Println("Before foo:", someValue)
    
    someValue, err := foo()
    if (err == nil) {
        fmt.Print("After foo:", someValue)
    }
}

Here we are assigning to the same someValue and declaring a new variable err at the same time with :=.

CodePudding user response：

For the sake of error detection, maybe you can add a nil check for the response variable as well. This might be a solution for you. For eq.

if response== nil {
    break
}

Please share your preferred or discovered answer to the situation.