On Fri, Jun 19, 2020 at 12:29 PM Iskander Sharipov <[email protected]> wrote: > > I used this to write something like a runtime in Go. > > https://play.golang.org/p/6jYw5L3fy0B > > I was wondering whether this code can break at some point.
I don't see any way that that code could break, but I agree that it does not follow the rules, so it is not guaranteed to always work. Ian > On Friday, June 19, 2020 at 10:04:01 PM UTC+3, Iskander Sharipov wrote: >> >> Hello! >> >> https://golang.org/src/runtime/symtab.go?s=7594:7745#L244 >> >> type Func struct { >> >> opaque struct{} // unexported field to disallow conversions >> >> } >> >> >> func (f *Func) raw() *_func { >> >> return (*_func)(unsafe.Pointer(f)) >> >> } >> >> >> An empty struct Func (T1) is converted to a non-zero struct _func (T2). >> >> From the unsafe.Pointer documentation >> (https://golang.org/pkg/unsafe/#Pointer): >> >> > T1->T2 conversion is safe if T2 is no larger than T1 ... (shortened for >> > clarity) >> >> I'm guessing that documentation probably meant "allocation size", not the >> "static type size"? >> T1 pointer can be obtained from the T2 allocation, so it's allocation size >> can be different from the unsafe.Sizeof(T1{}). >> >> Or it could be that runtime can violate that particular rule. >> >> My question: is it same to convert T1<->T2 even if sizeof(T1)<sizeof(T2), >> but the memory was allocated for the bigger object? >> >> Thank you in advance. >> >> >> > -- > 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 [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/fbeb324a-be55-4673-86a9-f6dc1046b0bco%40googlegroups.com. -- 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 [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAOyqgcWraFk_hrn%2BENC%3DWD%2BCLs_343hdONYhY%3D4myDNvuHatyQ%40mail.gmail.com.
