FAQ

On Tue, Feb 19, 2013 at 3:20 PM, Johann Höchtl wrote:

quick assignemnts, := , are meant to help the programmer and give the
language the feeling being a duck-typed, dynamic language yet with the
powers of static type checking. Unfortunately this feature comes at the
price of introducing nasty, hard to spot shadowing bugs.

Consider this program:

http://play.golang.org/p/nroI2nSKyG

package main

import "fmt"

func answertoeverything(idx int) bool {
return true
}

func main() {

var answer string
var found bool
for idx := range []int{1, 3, 5} {
if found := answertoeverything(idx); found == true {
answer = "We got an answer"
break
}
}

if found {
fmt.Println("The answer is", answer)
} else {
fmt.Println("No answer was found")
}
}

The variable "found" is hidden. This is clearly a mistake yet get's
unspotted by the current compiler. This is either a plain bug, or, if not,
I suppose to change the behaviour in that simply accessing a variable is
not enough to silence the compiler, but either assigning to it or taking
it'd address.

_ := silence

is seen very often and suffices to calm the compiler. I would suggest,
that only a proper assignment can silence the "introduced but not used"
error, or taking the address of such a variable as eg. in

callfunc(&notused)

Thus

_ := silence
would become
_ := &silence

If this variable get's actually used at a a later point, it is most
likely that it will not be used in a pointer context, in such as the
programmer can still benefit from the compilers analysis.
suppose we adopt this change, please write the update to the spec page and
explain it as simple and as clear as possible.

in what cases does the compiler give an error for shadowing? do you need to
add some exceptions to your rules?

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