On Mon, Nov 19, 2018 at 10:37 PM Robert Engels <reng...@ix.netcom.com> wrote: > That is not really true though, as I can declare a method that take a pointer > receiver and mutate through it, but the caller can pass a struct which it > thinks can not be mutated. > > https://play.golang.org/p/Abf4VX9kUTR
This is syntactic sugar for (&a).Change() - the method is still called on a pointer, even if it's not obvious from the code. It's one of the many ways in which `a.F()` differs from `A.F(a)`. I agree that it makes the mutability less obvious (there's a tradeoff between verbosity and convenience and Go deviates here), but it doesn't change what I said - if you pass a value to a function or method, it can't be mutated. > > Go isn’t type safe by stating that methods cannot mutate structs. Any reader > of the above code would think that couldn’t work, unless they inspected the > source to find a pointer receiver. > > On Nov 19, 2018, at 3:28 PM, Axel Wagner <axel.wagner...@googlemail.com> > wrote: > > The restriction has nothing to do with heaps (in fact, the Go language > (i.e. the spec) doesn't even have a concept of a "heap"). It's a > type-safety requirement. If you pass in a value, it can't be mutated, > full-stop. Reflect shouldn't allow you to bypass type-safety - only > "unsafe" can do that, hence the name. > On Mon, Nov 19, 2018 at 9:51 PM Robert Engels <reng...@ix.netcom.com> wrote: > > > Interesting. I guess that makes sense. But you would think that if using a > reflection call should force the compiler to heap allocate , then no reason > for the restriction. > > > On Nov 19, 2018, at 2:33 PM, Ian Denhardt <i...@zenhack.net> wrote: > > > Quoting Robert Engels (2018-11-19 15:13:53) > > But isn’t that just for safety. Meaning the unmarshall could use it as a > pointer via reflection and mutate it (but that is probably not what the > caller expects in Go) ? > > > No, see: > > > https://play.golang.org/p/MyF0Dx87-1j > > > If you pass in &foo instead and insert the appropriate call to > > value.Elem(), it works. > > > -- > > 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. > > For more options, visit https://groups.google.com/d/optout. > > > -- > > 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. > > For more options, visit https://groups.google.com/d/optout. -- 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. For more options, visit https://groups.google.com/d/optout.
