proposal: support "var identifier = _" to mute an identifier in certain scope.

[go101]

This is helpful to avoid using some identifiers which should be used in some scopes carelessly.

Example:

package main

func main(){
    var n = 123,
    // use n

    {
        // use n

        var n = _
        // now n disppears
    }

    // here, n is still alive
    // use n
}

[stemar94]

you can simply shadow your variables

var n = 123
{
    // use n

    n := n // or var n = n
    // now the real n can no longer be accessed
}
// here, n is still alive

https://play.golang.org/p/KOUBa5TVIv

[go101]

you can simply shadow your variables

it is not totally the same

[stemar94]

How about

const n = 1i // complex number

or

n_ := n
\\ no longer allowed to use/change n
if n != n_ {
    panic("n was modified")
}

I still don't get your use case.

[stemar94]

Maybe you want to solve it like this:
https://play.golang.org/p/r1cG8oPS8I

[cznic]

Put this into any of your *_test.go files

func use(...interface{}) {}

Silent the unused variable(s) error anywhere by writing

use(n, o, p)

Bonus: The program does not build when not testing.

[go101]

a more detailed example:

package main

func main(){
    var n = 123
    n++ // use n

    {
        n++ // use n

        var n = _ // this one will change spec few
        // now n disppears

        n++ // compiling error: n is undefined
    }

    // here, n is still alive
    n++ 

    var n = _ // // this one will change spec much
    // now n disppears

    n++ // compiling error: n is undefined

}

It is like the "unset" in some languages.

[mattn]

use unnamed vars

var n int
_ = n

var n int; _ = n

[stemar94]

I already got what you want to accomplish, but I don't get what it is good for.

[go101]

I already got what you want to accomplish, but I don't get what it is good for.

just let compiler report errors, just like the two error lines in my example. :)

[go101]

@mattn,

use unnamed vars

This is not my intention.

[go101]

@cznic, I don't get your code.

[stemar94]

@cznic, I don't get your code.

It's also only for using unused vars, so not what you want.

[bradfitz]

Sorry, previous discussions of overloading _ to mean new things (such as the zero value when _ is used on the RHS) have been rejected. This is similarly not an acceptable language change.

[go101]

@bradfitz, I think this one is more reasonable.

The underscore "_" is used in many cases now, but it is unnamed.
I think "deaf identifier" is a good name.

var _ = v // deaf variable can't hear anything

var v = _ // v becomes deaf too.

[go101]

@stemar94,

I already got what you want to accomplish, but I don't get what it is good for.

here is a useful case in reality:

func DoTrasaction(db *sql.DB, sqlStr string) error {
    tx, err := db.Begin()
    if err != nil {
        return err
    }

    var db = _
    // if db can be unset, then we can safely avoid misusing tx as db in following lines        

    // many callings of code
    // ...

    // we should call this
    tx.Exec(sqlStr)
    // but not this
    db.Exec(sqlStr) // if db is not unset, this line is ok
                    // for sql.DB and sql.Tx both has a same Exec method


    // ...

    err = tx.Commit()
    if err != nil {
        return err
    }

    return nil
}

[bradfitz]

You could do: db = nil. Or break the function up into smaller ones with more limited scopes.

[go101]

ye, there are some ways to avoid this problem, but the unset solution is cooler, ;)