[go-nuts] Re: Why is there no " declared and not used" compile error?
On Monday, 12 September 2016 08:57:15 UTC-4, Markus Zimmermann wrote: > > Hi gophers! > > I am wondering why we have a "declared and not used" compile error for > variables [https://play.golang.org/p/KLzHVO5L7q] but not for constants [ > https://play.golang.org/p/JG9dSa_VKg]? I am sure there is some rational > decision behind this that I have missed, but my Google-fu is just not > strong enough to find an answer. > I suspect the answer is: because unused constants and types cost nothing at run time. It's not that simple, of course, because constant and type declarations may be the only uses of an import of a package whose initialization has some cost; but this is quite marginal. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[go-nuts] Re: Why is there no " declared and not used" compile error?
On Monday, September 12, 2016 at 3:41:35 PM UTC+2, adon...@google.com wrote: > > On Monday, 12 September 2016 08:57:15 UTC-4, Markus Zimmermann wrote: >> >> Hi gophers! >> >> I am wondering why we have a "declared and not used" compile error for >> variables [https://play.golang.org/p/KLzHVO5L7q] but not for constants [ >> https://play.golang.org/p/JG9dSa_VKg]? I am sure there is some rational >> decision behind this that I have missed, but my Google-fu is just not >> strong enough to find an answer. >> > > I suspect the answer is: because unused constants and types cost nothing > at run time. It's not that simple, of course, because constant and type > declarations may be the only uses of an import of a package whose > initialization has some cost; but this is quite marginal. > The const declaration of my example is inside an unexported function body. It can not be accessed by an import. So, it should really matter only at compile time, right? However, I am referring to the definition of https://golang.org/doc/faq#unused_variables_and_imports which states "... Go refuses to compile programs with unused variables or imports, trading short-term convenience for long-term build speed and program clarity." Which holds true in the same way for an unused const as it does for an unused variable. However, even though it produces the same results, i.e. a new declaration which decreases the program clarity, only the variable declaration is marked. Additionally, if an unused constant is compiled into the binary it does also matter to the binary size, even just a little bit. Cheers, Markus -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[go-nuts] Re: Why is there no " declared and not used" compile error?
On Monday, September 12, 2016 at 3:21:50 PM UTC+2, Sjon Kosse wrote: > > Hello, > > Const values can be accesed still by reflection in a reasonable manner. > This question has come by quite a few times before on the mailing list, > better explanations should be easy to find. > I do not think that this is true. Wouldn't this already break the first reflection law? How can you examine something with the reflection package without mentioning it in the source code? Where would the interface value come from? Additionally, my example does not export anything, it is a constant inside an unexported function. Cheers, Markus -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[go-nuts] Re: Why is there no " declared and not used" compile error?
On 13 September 2016 at 08:22, Markus Zimmermann wrote:
> On Monday, September 12, 2016 at 3:41:35 PM UTC+2, adon...@google.com
> wrote:
>>
>> unused constants and types cost nothing at run time. It's not that
>> simple, of course, because constant and type declarations may be the only
>> uses of an import of a package whose initialization has some cost; but this
>> is quite marginal.
>>
>
> The const declaration of my example is inside an unexported function body.
> It can not be accessed by an import. So, it should really matter only at
> compile time, right?
>
Right. The import case I was referring to is this:
import "p"
func main() {
const unused = p.K
}
The unused constant causes p to be an (unnecessary) dependency, which in
turn causes p.init to be executed.
However, I am referring to the definition of https://golang.org/doc/faq#
> unused_variables_and_imports which states "... Go refuses to compile
> programs with unused variables or imports, trading short-term convenience
> for long-term build speed and program clarity." Which holds true in the
> same way for an unused const as it does for an unused variable. However,
> even though it produces the same results, i.e. a new declaration which
> decreases the program clarity, only the variable declaration is marked.
>
You are right that the motivation given in the FAQ should apply equally to
constants and types.
Additionally, if an unused constant is compiled into the binary it does
> also matter to the binary size, even just a little bit.
An unused constant is unlikely to affect the size of the final executable
since in a typical compiler generates code or data for a constant only when
it is used. It will be present in the intermediate .a files though.
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[go-nuts] Re: Why is there no " declared and not used" compile error?
On Tuesday, September 13, 2016 at 3:50:12 PM UTC+2, Alan Donovan wrote:
>
> On 13 September 2016 at 08:22, Markus Zimmermann > wrote:
>
>> On Monday, September 12, 2016 at 3:41:35 PM UTC+2, adon...@google.com
>> wrote:
>>>
>>> unused constants and types cost nothing at run time. It's not that
>>> simple, of course, because constant and type declarations may be the only
>>> uses of an import of a package whose initialization has some cost; but this
>>> is quite marginal.
>>>
>>
>> The const declaration of my example is inside an unexported function
>> body. It can not be accessed by an import. So, it should really matter only
>> at compile time, right?
>>
>
> Right. The import case I was referring to is this:
>
> import "p"
> func main() {
> const unused = p.K
> }
>
> The unused constant causes p to be an (unnecessary) dependency, which in
> turn causes p.init to be executed.
>
This holds true for every declaration with an initialization, and should be
therefore be no reason to allow such unused constant declarations. There is
also already the official idiom to use the blank identifier as the explicit
package name if someone really needs p.init to be executed.
However, I am referring to the definition of
>> https://golang.org/doc/faq#unused_variables_and_imports which states
>> "... Go refuses to compile programs with unused variables or imports,
>> trading short-term convenience for long-term build speed and program
>> clarity." Which holds true in the same way for an unused const as it does
>> for an unused variable. However, even though it produces the same results,
>> i.e. a new declaration which decreases the program clarity, only the
>> variable declaration is marked.
>>
>
> You are right that the motivation given in the FAQ should apply equally to
> constants and types.
>
Do you think this might be worth bringing up in golang-dev?
Additionally, if an unused constant is compiled into the binary it does
>> also matter to the binary size, even just a little bit.
>
>
> An unused constant is unlikely to affect the size of the final executable
> since in a typical compiler generates code or data for a constant only when
> it is used. It will be present in the intermediate .a files though.
>
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[go-nuts] Re: Why is there no " declared and not used" compile error?
On 14 September 2016 at 09:32, Markus Zimmermann wrote: > > Do you think this might be worth bringing up in golang-dev? > No. We can't make this change to the language without breaking existing programs. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[go-nuts] Re: Why is there no " declared and not used" compile error?
On Monday, September 12, 2016 at 8:57:15 AM UTC-4, Markus Zimmermann wrote: > > Hi gophers! > > I am wondering why we have a "declared and not used" compile error for > variables [https://play.golang.org/p/KLzHVO5L7q] but not for constants [ > https://play.golang.org/p/JG9dSa_VKg]? I am sure there is some rational > decision behind this that I have missed, but my Google-fu is just not > strong enough to find an answer. > > Cheers, > Markus > It may be a stretch, but allowing unused constants may be desirable when we're using iota and we don't want higher constants to change when some of the intermediate values become unused. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[go-nuts] Re: Why is there no " declared and not used" compile error?
On Wednesday, September 14, 2016 at 3:47:29 PM UTC+2, Chris Hines wrote: > > On Monday, September 12, 2016 at 8:57:15 AM UTC-4, Markus Zimmermann wrote: >> >> Hi gophers! >> >> I am wondering why we have a "declared and not used" compile error for >> variables [https://play.golang.org/p/KLzHVO5L7q] but not for constants [ >> https://play.golang.org/p/JG9dSa_VKg]? I am sure there is some rational >> decision behind this that I have missed, but my Google-fu is just not >> strong enough to find an answer. >> >> Cheers, >> Markus >> > > It may be a stretch, but allowing unused constants may be desirable when > we're using iota and we don't want higher constants to change when some of > the intermediate values become unused. > No reason to keep an unused constant for that. You can use the blank identifier https://play.golang.org/p/A55mWz_c93 -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[go-nuts] Re: Why is there no " declared and not used" compile error?
On Wednesday, September 14, 2016 at 3:37:10 PM UTC+2, Alan Donovan wrote: > > On 14 September 2016 at 09:32, Markus Zimmermann > wrote: >> >> Do you think this might be worth bringing up in golang-dev? >> > > No. We can't make this change to the language without breaking existing > programs. > That is unfortunately. I will just write a linter check for that. Thanks for the talk! -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[go-nuts] Re: Why is there no " declared and not used" compile error?
Am Mittwoch, 14. September 2016 15:43:14 UTC+2 schrieb Markus Zimmermann: > > On Wednesday, September 14, 2016 at 3:37:10 PM UTC+2, Alan Donovan wrote: >> >> On 14 September 2016 at 09:32, Markus Zimmermann >> wrote: >>> >>> Do you think this might be worth bringing up in golang-dev? >>> >> >> No. We can't make this change to the language without breaking existing >> programs. >> > > That is unfortunately. I will just write a linter check for that. Thanks > for the talk! > I think it is perfectly fine to have constants which are unused inside a package: A package exporting just a bunch of physical constants (think of c, alpha, h, ...) but not using any of them seems useful and not a sign of an error or even a hint for current or future problems. Regarding UNexported constants: I could imagine myself defining some physical constants from other constants, e.g. const RK = 25812.8074555 const rk = h/(e*e) with the exported RK the official measured value and rk the value as computed (from other constants). Now rk serves as a nice documentation and test can compare RK and rk and do some sanity checking (for this rk could live in a _test.go file, I know and would be used.) V. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[go-nuts] Re: Why is there no " declared and not used" compile error?
A difference: - it isn't possible to derive the address of a named variable from the address of another named variable - it is possible to derive the value of a named const from another named const const ( a = 0 // b-1, c-2 b = 1 // a+1, c-1 c = 2 // a+2, b+1 ) Reflection needs to be put aside because it can be made to access almost anything we want. On Monday, September 12, 2016 at 2:57:15 PM UTC+2, Markus Zimmermann wrote: > > Hi gophers! > > I am wondering why we have a "declared and not used" compile error for > variables [https://play.golang.org/p/KLzHVO5L7q] but not for constants [ > https://play.golang.org/p/JG9dSa_VKg]? I am sure there is some rational > decision behind this that I have missed, but my Google-fu is just not > strong enough to find an answer. > > Cheers, > Markus > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
[go-nuts] Re: Why is there no " declared and not used" compile error?
what about when you're writing a lib, can't the importing code make use of constants? On Monday, 12 September 2016 13:57:15 UTC+1, Markus Zimmermann wrote: > > Hi gophers! > > I am wondering why we have a "declared and not used" compile error for > variables [https://play.golang.org/p/KLzHVO5L7q] but not for constants [ > https://play.golang.org/p/JG9dSa_VKg]? I am sure there is some rational > decision behind this that I have missed, but my Google-fu is just not > strong enough to find an answer. > > Cheers, > Markus > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [go-nuts] Re: Why is there no " declared and not used" compile error?
On Wed, Sep 14, 2016 at 6:43 AM, Markus Zimmermann wrote: > On Wednesday, September 14, 2016 at 3:37:10 PM UTC+2, Alan Donovan wrote: >> >> On 14 September 2016 at 09:32, Markus Zimmermann wrote: >>> >>> Do you think this might be worth bringing up in golang-dev? >> >> >> No. We can't make this change to the language without breaking existing >> programs. > > > That is unfortunately. I will just write a linter check for that. Thanks for > the talk! Personally I feel like an unused variable normally indicates a problem. You set the variable to something, but you never used it. Why not? There is simply no reason to have an unused variable. An unused constant does not normally indicate a problem. Constants can be documentation. They can mean "this value means this" even if the value is never actually used. I think it's uncommon for an unused constant to indicate a programming error. Fortunately, this is a question that can be determined empirically. Write the code to detect unused constants. Run it over a diverse code base, such as a bunch of github repos. See how many actual bugs it detects. Actual data can help decide whether this is worth doing. Ian -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
Re: [go-nuts] Re: Why is there no " declared and not used" compile error?
On Wed, Sep 14, 2016 at 11:51 AM, 'simon place' via golang-nuts wrote: > what about when you're writing a lib, can't the importing code make use of > constants? No warning about an unused variable or constant would ever apply to an exported name. That would not make sense. Ian > On Monday, 12 September 2016 13:57:15 UTC+1, Markus Zimmermann wrote: >> >> Hi gophers! >> >> I am wondering why we have a "declared and not used" compile error for >> variables [https://play.golang.org/p/KLzHVO5L7q] but not for constants >> [https://play.golang.org/p/JG9dSa_VKg]? I am sure there is some rational >> decision behind this that I have missed, but my Google-fu is just not strong >> enough to find an answer. >> >> Cheers, >> Markus > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
