On Wed, 19 Jun 2024 at 22:43, Oliver Eikemeier <eikeme...@gmail.com> 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 it that way. I would interpret it as *“taking pointer > to distinct zero-size variables may or may not result in equal pointers”*. > > But not being able to have a *repeatable* result of a pointer comparison > seems strange to me. The specification says “you'll get *some* pointers”. > Fine. > The spec says both. It says > Two distinct zero-size variables may have the same address in memory. And it says > Pointers to distinct zero-size variables may or may not be equal. The former means what you say. The latter means what Ian says. Then I have two pointers. Where in the spec is “the result of comparison of > pointers may change over time”? > > For example (Go Playground <https://go.dev/play/p/acknRHBvi0P>): > > func f3() { > var ( > a struct{} > b int > aa = unsafe.Pointer(&a) > ba = unsafe.Pointer(&b) > eq = aa == ba > ) > > println("&a:", aa) > println("&b:", ba) > println("&a == &b:", eq) > } > > gives > > &a: 0xc000046738 > &b: 0xc000046738 > &a == &b: false > > and &b is not even a pointer to a zero-sized variable. > > Could be true, could be false, could change each time you > do the comparison. So this behavior is permitted by the spec. > > > I'm not sure about the “undefined behavior *over time*”. I get that the > compiler lays out the memory however it sees fit, but then I should have > unchanging values in my variables. > > > > The interesting part here is that I can create two pointers (which may > or may not be equal per specification), but depending on how I compare them > I get different results. > > Yes, as the spec permits. > > > I assume this has little relevance in practice, but it is surprising. > > -- > 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. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/64e58302-59a6-4cbf-859e-aa6b8a2b6068n%40googlegroups.com > <https://groups.google.com/d/msgid/golang-nuts/64e58302-59a6-4cbf-859e-aa6b8a2b6068n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- 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. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAEkBMfE6bzYQJ7s_GHEN7%3Dp3s2p0pSWNMgcw8t4tTiSy04ucFg%40mail.gmail.com.
