How to avoid annoying error "declared and not used"

I ran into this while I was learning Go 2 years ago, so I declared my own function.

// UNUSED allows unused variables to be included in Go programs
func UNUSED(x ...interface{}) {}

And then you can use it like so:

UNUSED(x)
UNUSED(x, y)
UNUSED(x, y, z)

The great thing about it is, you can pass anything into UNUSED.

Is it better than the following?

_, _, _ = x, y, z

That's up to you.

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)
}

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.