It's worth noting that before the Unmarshal v is {}(main.S) and afterwards
{}(map[string]interface{})
On Wednesday, April 24, 2024 at 6:46:18 PM UTC+2 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 :)
>
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