Support interface in As/InvokeAs

[d-enk]

I suggest using something like:

func canCast[FROM, TO any](soft bool) bool {
	var from FROM
	anyFrom := any(from)

	if anyFrom == nil { // check for interface by reflect
		typeFrom := reflect.TypeOf(&from).Elem()
		typeTo := reflect.TypeOf((*TO)(nil)).Elem()

		toInterface := typeTo.Kind() == reflect.Interface

		return toInterface && typeFrom.Implements(typeTo) ||

			// interface -> not interface - maybe false positive when real FROM not TO
			soft && !toInterface && typeTo.Implements(typeFrom)
	}

	_, ok := anyFrom.(TO)

	return ok
}

instead simply:

var from FROM
_, ok := any(from).(TO)

For As just call canCast[Initial, Alias]

do/di_alias.go

Lines 25 to 26 in 1998a7a

	_, ok := any(empty[Initial]()).(Alias)
	if !ok {

For InvokeAs apparently need getInstanceType() reflect.Type method

do/service.go

Lines 131 to 133 in 1998a7a

	if svc, ok := service.(serviceGetEmptyInstance); ok {
	// we need an empty instance here, because we don't want to instantiate the service when not needed
	if _, ok = svc.getEmptyInstance().(T); ok {

[d-enk]

soft flag includes checking whether TO type (not interface) can be in FROM interface
looks like a very rare case, but still happens

in case of As you can rely on the provider's error

do/service_alias.go

Lines 161 to 166 in 1998a7a

	switch service.getEmptyInstance().(type) {
	case Alias:
	return service.shutdown(ctx)
	default:
	return fmt.Errorf("DI: could not cast `%s` as `%s`", s.targetName, s.name)
	}