Re: [go-nuts] Why constant is not addressable in golang?
On Mon, Aug 21, 2017 at 12:56:19PM +, Jan Mercl wrote: >> That is >> >> const onethird = 1 / 3 >> >> has greater precision than >> >> onethird := float64(1) / 3 > > Zero does not seem to have greater precision than 0. when > approximating the real number 1/3. IMHO, the less smart-ass responses the list would see, the better. But I see your point, thanks. To the OP: the first statement should have been const onethird = 1.0 / 3 instead. By the way, currently defined limits the compliant Go compilers must support with regard to constants, can be found in [1]. 1. https://golang.org/ref/spec#Constants -- 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] Why constant is not addressable in golang?
On Mon, Aug 21, 2017 at 1:46 PM Konstantin Khomoutov wrote: > That is > > const onethird = 1 / 3 > > has greater precision than > > onethird := float64(1) / 3 Zero does not seem to have greater precision than 0. when approximating the real number 1/3. -- -j -- 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] Why constant is not addressable in golang?
On Sun, Aug 20, 2017 at 10:23:27PM -0700, chou wrote: > I guess that const will be substitute literally at compile time > for performance improvements. So there is not such variable in > run time. > > Is it right? One of the reasons for this is that constants in Go have properties which set them apart from values: - For numerics, they are allowed (and enforced to a certain extent) to have size and/or precision way larger than of the regular types supported by the language. That is const onethird = 1 / 3 has greater precision than onethird := float64(1) / 3 and this may affect calculations done on floating-point numbers. See for instance [2] for a recent example on why this matters. [3] is an in-depth explanation of those effects, and [4] is a gentler one. - Constant are "almost typeless": they have default type for their literal value (say, int for the literal 42 or string for the literal "42") but the compiler allows a much greater freedom when you assign a constant to a variable (which has exact type). Say, in Go, it's impossible to do i := 0 uint32 j := i but it's perfectly valid to do const i = 0 uint32 j := i As you can see, having these properties appears to be incompatible with actually storing the values of the constants in some R/O memory and making them addressable. Please read [1] to get full grasp on constants in Go. 1. https://blog.golang.org/constants 2. https://groups.google.com/d/topic/golang-nuts/XP-_nRWjKnM/discussion 3. http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html 4. http://floating-point-gui.de/ -- 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] Why constant is not addressable in golang?
> May I ask why it would be interesting to take the address of a constant? I have been already faced to this case. I usually use go swagger to generate the model from swagger spec. Go swagger generates some structure with field pointer (for example for string) where I always put the same value. The workaround, that I usually use, is to use global variable instead of global constant. -- 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] Why constant is not addressable in golang?
Thanks for your explaination, I was just curious about the language constraint details. 在 2017年8月21日星期一 UTC+8下午2:16:25，Axel Wagner写道： > > If a constant was addressable, you could do > > const x = 42 > x = 23 > fmt.Println(x) // 23 > > so a constant wouldn't be constant anymore. The minimum Go would need, to > make constants addressable would be some notion of const-pointers (that is, > pointers which don't allow modification of the pointee). > > May I ask why it would be interesting to take the address of a constant? > > On Mon, Aug 21, 2017 at 7:23 AM, chou > > wrote: > >> I guess that const will be substitute literally at compile time >> for performance improvements. So there is not such variable in >> run time. >> >> Is it right? >> >> -- >> 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...@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.
Re: [go-nuts] Why constant is not addressable in golang?
If a constant was addressable, you could do const x = 42 x = 23 fmt.Println(x) // 23 so a constant wouldn't be constant anymore. The minimum Go would need, to make constants addressable would be some notion of const-pointers (that is, pointers which don't allow modification of the pointee). May I ask why it would be interesting to take the address of a constant? On Mon, Aug 21, 2017 at 7:23 AM, chou wrote: > I guess that const will be substitute literally at compile time > for performance improvements. So there is not such variable in > run time. > > Is it right? > > -- > 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.
[go-nuts] Why constant is not addressable in golang?
I guess that const will be substitute literally at compile time for performance improvements. So there is not such variable in run time. Is it right? -- 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.
