package main
import "fmt"
type intr interface {
String() string
}
type bar struct{}
func (b *bar) String() string {
return "bar"
}
type foo struct {
bar *intr
}
func main() {
bar1 := bar{}
foo1 := foo{bar: &bar1}
fmt.Println(foo1)
}
I get a compile-time error:
cannot use &bar1 (type *bar) as type *intr in field value: *intr is pointer to interface, not interface
Why is this error happened?
How to assign foo.bar?
You're assigning it to a pointer to the interface. After changing the field type to interface it will work:
type foo struct {
bar intr
}
Pointers to interfaces are quite rarely needed.
Uber-go style guide pointers-to-interfaces contains exact answer to your question,
You almost never need a pointer to an interface. You should be passing interfaces as values—the underlying data can still be a pointer. An interface is two fields: A pointer to some type-specific information. You can think of this as "type." And a data pointer. If the data stored is a pointer, it’s stored directly. If the data stored is a value, then a pointer to the value is stored. If you want interface methods to modify the underlying data, you must use a pointer.
My recommendation is to get acquainted with it as soon as possible,
Hope it helps
