Many thanks Ian! On Friday, June 19, 2020 at 11:32:19 PM UTC+3, Ian Lance Taylor wrote: > > On Fri, Jun 19, 2020 at 12:29 PM Iskander Sharipov <[email protected] > <javascript:>> 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] <javascript:>. > > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/fbeb324a-be55-4673-86a9-f6dc1046b0bco%40googlegroups.com. > > >
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