Fix "declared and not used" message in Golang [SOLVED]

In this tutorial, we will walk through some examples of avoiding error "declared and not used" in Golang. If a variable is defined in the Go programming language but not used in the code, the compiler will display the error "declared and not used" We must eliminate any unnecessary packages or variables from the code in accordance with best practices for programming. Memory, compilation, and execution time will be saved.

You can avoid removing those unnecessary variables or packages by using the blank identifier (_).

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Take a look at the examples below:

 

Example 1: Error - "imported and not used"

Here we have a sample go code:

package main

import (
	"fmt"
	"encoding/json"
)

func main() {
	name := "GoLinuxCloud"
	age := 1
	fmt.Println("My name is:", name, "and my age is: ", age)
}

In the above code, two packages <span class="w3-codespan">fmt</span> and encoding/json are imported but encoding/jsonwas not used. So the following error will return:

# command-line-arguments
.\milestone8.go:5:2: imported and not used: "encoding/json"

 

Fix imported and not used

We ca use a blank identifier (_) before the package name that will not be used as following code:

package main

import (
	"fmt"
	_ "encoding/json"
)

func main() {
	name := "GoLinuxCloud"
	age := 1
	fmt.Println("My name is:", name, "and my age is:", age)
}

Output:

My name is: GoLinuxCloud and my age is: 1

 

Example 2: Error - "declared and not used"

Here we have another go code:

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package main

import (
	"fmt"
)

func main() {
	page := "GolinuCloud"
	author := "Anonymous Author"

	fmt.Println("Name is:", page)
}

In the above code, two variables page and author are declared but author was not used. So the following error will return.

# command-line-arguments
.\milestone8.go:9:2: author declared but not used

 

Fix declared but not used

To avoid this error we can assign the variable to a blank identifier (_) as the following code:

package main

import (
	"fmt"
)

func main() {
	page := "GolinuCloud"
	author := "Anonymous Author"

	fmt.Println("Page is:", page)
	_ = author
}

Output:

Page is: GolinuCloud

 

Example 3: Variable declared and used but still getting “declared but not used”

In the below example, the variable is used but the program still arise declared but not used error:

package main

import "fmt"

func main(){
    var boolStr string

    if false {
        boolStr := "False"
    }else{
        boolStr := "True"
    }

    fmt.Println(boolStr) // variable used
}

Because the variable boolStris being re-declared in the if-else block of the code, it returns the error. Any variables declared using := are local in the go programming language, meaning they can only be utilized inside the specific block or function. The code fails because the variable is not used in the specific if-else block range. To solve this problem, you just need to assign new values to the global variable boolStr instead of declaring them again, as shown below:

package main

import "fmt"

func main(){
    var boolStr string // declared global variable

    if false {
        boolStr = "False" // asign value, not declare again
    }else{
        boolStr = "True"
    }

    fmt.Println(boolStr) // variable used
}

Output:

True

 

Summary

In this article, I have provided some example of how to eliminate declare but not used error. The presence of an unused variable may indicate a bug, while unused imports just slow down compilation. Accumulate enough unused imports in your code tree and things can get very slow. For these reasons, Go allows neither.

To avoid these compilation errors I recommend using Visual Studio Code for GO IDE which will warn you about these errors even before you compile and run your code.

 

References

https://go.dev/doc/effective_go#blank

 

Categories GO

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