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 <eike...@fillmore-labs.com> 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 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. 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.
