hi there,
I am playing a bit with generics.
I am trying to implement a parametrized "Read" function that unmarshals
bytes into some type value that implements an interface:
type T1 struct {
v string
}
func (t *T1) UnmarshalBinary(p []byte) error {
t.v = string(p)
return nil
}
type Unmarshaler interface {
UnmarshalBinary(p []byte) error
}
func f1[T Unmarshaler](p []byte) (T, error) {
var t T
err := t.UnmarshalBinary(p)
return t, err
}
func main() {
p := []byte("hello")
t1, err := f1[T1](p)
if err != nil {
log.Panic(err)
}
log.Printf("t1: %+v", t1)
}
my naive attempt failed like so:
./prog.go:26:16: T1 does not implement Unmarshaler (UnmarshalBinary method has
pointer receiver)
it's only when I rewrite my f1 function like so that it "works":
func f2[T any](p []byte) (t T, err error) {
switch t := any(&t).(type) {
case Unmarshaler:
err = t.UnmarshalBinary(p)
default:
panic("boo")
}
return t, err
}
but it doesn't take advantage of the nice type constraints Go's generics
provide.
of course, replacing:
t1, err := f1[T1](p)
with:
t1, err := f1[*T1](p)
compiles. but fails at runtime.
what am I missing?
how do I convey the constraint "unmarshaling usually imply passing a
pointer to some value" ?
-s
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