How to avoid annoying error "declared and not used"

Solution 1:

That error is here to force you to write better code, and be sure to use everything you declare or import. It makes it easier to read code written by other people (you are always sure that all declared variables will be used), and avoid some possible dead code.

But, if you really want to skip this error, you can use the blank identifier (_) :

package main

import (
    "fmt" // imported and not used: "fmt"
)

func main() {
    i := 1 // i declared and not used
}

becomes

package main

import (
    _ "fmt" // no more error
)

func main() {
    i := 1 // no more error
    _ = i
}

As said by kostix in the comments below, you can find the official position of the Go team in the FAQ:

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.

Solution 2:

You can use a simple "null function" for this, for example:

func Use(vals ...interface{}) {
    for _, val := range vals {
        _ = val
    }
}

Which you can use like so:

package main

func main() {
    a := "declared and not used"
    b := "another declared and not used"
    c := 123

    Use(a, b, c)
}

There's also a package for this so you don't have to define the Use function every time:

import (
  "github.com/lunux2008/xulu"
)

func main() {
  // [..]

  xulu.Use(a, b, c)
}

Solution 3:

According to the FAQ:

Some have asked for a compiler option to turn those checks off or at least reduce them to warnings. Such an option has not been added, though, because compiler options should not affect the semantics of the language and because the Go compiler does not report warnings, only errors that prevent compilation.

There are two reasons for having no warnings. First, if it's worth complaining about, it's worth fixing in the code. (And if it's not worth fixing, it's not worth mentioning.) Second, having the compiler generate warnings encourages the implementation to warn about weak cases that can make compilation noisy, masking real errors that should be fixed.

I don't necessarily agree with this for various reasons not worth going into. It is what it is, and it's not likely to change in the near future.

For packages, there's the goimports tool which automatically adds missing packages and removes unused ones. For example:

# Install it
$ go get golang.org/x/tools/cmd/goimports

# -w to write the source file instead of stdout
$ goimports -w my_file.go

You should be able to run this from any half-way decent editor − for example for Vim:

:!goimports -w %

The goimports page lists some commands for other editors, and you typically set it to be run automatically when you save the buffer to disk.

Note that goimports will also run gofmt.

As was already mentioned, for variables the easiest way is to (temporarily) assign them to _ :

// No errors
tasty := "ice cream"
horrible := "marmite"

// Commented out for debugging
//eat(tasty, horrible)

_, _ = tasty, horrible

How to avoid annoying error "declared and not used"

Solution 1:

Solution 2:

Solution 3:

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