> In the first case, the interface contains a value of type S, which is not writable. The value contained in the interface is not addressable.
Thank you for the quick feedback. Why is that? Memory for val has been allocated and val is passed by value (hence copied). Why is that copy not be addressable? On Wednesday, April 24, 2024 at 6:51:21 PM UTC+2 burak serdar wrote: > In the first case, the interface contains a value of type S, which is > not writable. The value contained in the interface is not addressable. > So Unmarshal creates a new map and fills that. In the second case the > interface contains *S, which is writable, so unmarshal fills it in via > reflection. > > On Wed, Apr 24, 2024 at 10:46 AM cpu...@gmail.com <cpu...@gmail.com> > wrote: > > > > Every time I feel I've come to terms with how Go works I round a corner > and hit a wall, even after doing this for >5 years. Here's one. > > > > Consider this simple code (https://go.dev/play/p/bph5I80vc99): > > > > package main > > > > import ( > > "encoding/json" > > "fmt" > > ) > > > > type S struct { > > Foo int > > } > > > > func update(v any) { > > if err := json.Unmarshal([]byte(`{"Foo": 42}`), &v); err != nil { > > panic(err) > > } > > fmt.Printf("%v %T\n", v, v) > > } > > > > func main() { > > var val S > > > > // map[Foo:42] map[string]interface {} > > update(val) > > > > // &{42} *main.S > > update(&val) > > } > > > > Why would calling by value change the type of the value passed to map? I > would expect an interface with a dynamic type of main.S, but its > map[string]interface{}, or json.Unmarshal makes it so. > > > > Insights appreciated :) > > > > -- > > 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...@googlegroups.com. > > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/980466d2-1686-4b79-aec1-45b592db2caan%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 golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/ec00ba73-b91e-4a1c-a5ed-4d5507a90c18n%40googlegroups.com.
