Re: [go-nuts] Comparison of pointers to distinct zero-sized variables

On Tue, Jun 25, 2024 at 9:37 PM 'Axel Wagner' via golang-nuts wrote: > > you might be interested to learn that Ian has filed a CL adding an FAQ entry. Now committed at https://go.dev/doc/faq#zero_size_types . Ian -- You received this message because you are subscribed to the Google Groups

Re: [go-nuts] Comparison of pointers to distinct zero-sized variables

Hi, you might be interested to learn that Ian has filed a CL adding an FAQ entry . On Thu, 20 Jun 2024 at 16:18, Oliver Eikemeier wrote: > Thanks for that example. > > The issue is that you and I have constructed aliased variables that the

Re: [go-nuts] Comparison of pointers to distinct zero-sized variables

I want to re-emphasise that both of these examples violate the allowed usages of unsafe.Pointer defined by gc. So I would argue that, yes, its expectation is reasonable, because it explicitly told you not to create this situation. If you can construct a program that does not violate the

Re: [go-nuts] Comparison of pointers to distinct zero-sized variables

> Am 20.06.2024 um 14:12 schrieb Axel Wagner : > > On Thu, 20 Jun 2024 at 13:48, Oliver Eikemeier > wrote: > > I think you should acknowledge that the spec *is* already trying to be very > clear about this. The fact that you can poke holes in it is because

Re: [go-nuts] Comparison of pointers to distinct zero-sized variables

What I asked did not require the first, I was referring more about the latter. So regardless of how it is implemented it is always false. On Jun 20, 2024, at 7:39 AM, Axel Wagner wrote:On Thu, 20 Jun 2024 at 14:21, Robert Engels wrote:I would add that I think the Go team

Re: [go-nuts] Comparison of pointers to distinct zero-sized variables

FYI, filed https://github.com/golang/go/issues/68086 for the spec-hole that conversions between unsafe.Pointer and other pointer types are not implementation defined. On Thu, 20 Jun 2024 at 14:12, Axel Wagner wrote: > > > On Thu, 20 Jun 2024 at 13:48, Oliver Eikemeier < >

Re: [go-nuts] Comparison of pointers to distinct zero-sized variables

I would add that I think the Go team should strive to remove as much “implementation defined” or “undefined” from the spec as possible. Forgo the optimizations. It’s this language that makes C++ such a pain to work with especially in a cross platform manner. I think you can safely narrow the spec

Re: [go-nuts] Comparison of pointers to distinct zero-sized variables

On Thu, 20 Jun 2024 at 13:48, Oliver Eikemeier wrote: > > Am 20.06.2024 um 13:24 schrieb Axel Wagner >: > > We can see that 1. `unsafe.Pointer` is definitionally a pointer type, 2. > in your example, the two `unsafe.Pointers` do not point to the same > variable and do not have the value `nil`

Re: [go-nuts] Comparison of pointers to distinct zero-sized variables

> Am 20.06.2024 um 13:24 schrieb Axel Wagner : > > We can see that 1. `unsafe.Pointer` is definitionally a pointer type, 2. in > your example, the two `unsafe.Pointers` do not point to the same variable and > do not have the value `nil` and 3. are not pointing at distinct zero-sized >

Re: [go-nuts] Comparison of pointers to distinct zero-sized variables

On Thu, Jun 20, 2024 at 1:26 PM 'Axel Wagner' via golang-nuts wrote: > (apologies for the abundance of grammatical and spelling errors that occurred > during editing and of course only became visible after hitting "send") (Send collapses the wave function ;-) -- You received this message

Re: [go-nuts] Comparison of pointers to distinct zero-sized variables

(apologies for the abundance of grammatical and spelling errors that occurred during editing and of course only became visible after hitting "send") On Thu, 20 Jun 2024 at 13:24, Axel Wagner wrote: > On Thu, 20 Jun 2024 at 12:28, Oliver Eikemeier < > eikeme...@fillmore-labs.com> wrote: > >> Let

Re: [go-nuts] Comparison of pointers to distinct zero-sized variables

On Thu, Jun 20, 2024 at 1:16 PM Oliver Eikemeier wrote: > • Pointer types are comparable. Two pointer values are equal if they point to > the same variable or if both have value nil. Pointers to distinct zero-size > variables may or may not be equal. Compare to (made up) "NaNs always compare

Re: [go-nuts] Comparison of pointers to distinct zero-sized variables

On Thu, 20 Jun 2024 at 12:28, Oliver Eikemeier wrote: > Let me start with this: I’m fine with the behavior, it is exotic enough > that even the optimizer should be allowed to assume something that doesn’t > hold during runtime, since it simplifies things. > > What I think is at least surprising

Re: [go-nuts] Comparison of pointers to distinct zero-sized variables

https://go.dev/ref/spec#Comparison_operators • Pointer types are comparable. Two pointer values are equal if they point to the same variable or if both have value nil. Pointers to distinct zero-size variables may or may not be equal. Another example (Go Playground

Re: [go-nuts] Comparison of pointers to distinct zero-sized variables

On Thu, Jun 20, 2024 at 12:28 PM Oliver Eikemeier wrote: > It mentions “pointers” (plural) to zero-sized variables, but for this > behavior it is sufficient when only one pointer derives from a pointer to a > zero-sized variable, as demonstrated in the example below. The plural is there

Re: [go-nuts] Comparison of pointers to distinct zero-sized variables

Let me start with this: I’m fine with the behavior, it is exotic enough that even the optimizer should be allowed to assume something that doesn’t hold during runtime, since it simplifies things. What I think is at least surprising and at worst lacking is the documentation. It mentions

Re: [go-nuts] Comparison of pointers to distinct zero-sized variables

On Wed, 19 Jun 2024 at 22:43, Oliver Eikemeier wrote: > The specs says, as you say above, "Pointers to distinct zero-size > variables may or may not be equal.” That means that you can't predict > the result of any given comparison of addresses of zero-sized > variables. > > > I'm not sure I read

Re: [go-nuts] Comparison of pointers to distinct zero-sized variables

Hi, Ian Lance Taylor schrieb am Mittwoch, 19. Juni 2024 um 19:19:09 UTC+2: On Wed, Jun 19, 2024 at 9:59 AM Oliver Eikemeier wrote: > The specification says: “Pointers to distinct zero-size variables may or may not be equal.” The specs says, as you say above, "Pointers to distinct

Re: [go-nuts] Comparison of pointers to distinct zero-sized variables

On Wed, Jun 19, 2024 at 9:59 AM Oliver Eikemeier wrote: > > I'm observing some strange behavior and could use some help understanding it. > > The specification says: “Pointers to distinct zero-size variables may or may > not be equal.” > > With the following program (Go Playground): > > var ( a

[go-nuts] Comparison of pointers to distinct zero-sized variables

I'm observing some strange behavior and could use some help understanding it. The specification says: *“Pointers to distinct zero-size variables may or may not be equal.”* With the following program (Go Playground