MakeFunc.go

func MakeFunc(out any) error {

  handle := func(args []any) ([]any, error) {
    // the func we're wrapping
    return args
  }

	outFn := reflect.ValueOf(out).Elem()
	outType := outFn.Type()

	numOut := outType.NumOut()
	lastIsError := false

	if numOut > 0 {
		lastArg := outType.Out(numOut - 1)
		lastIsError = lastArg == typeOfError
	}

	newFn := reflect.MakeFunc(outType, func(in []reflect.Value) []reflect.Value {
		arg := make([]any, len(in))
		for i, a := range in {
			arg[i] = a.Interface()
		}

		result, err := handle(arg...)

		out := make([]reflect.Value, numOut)
		for i := range out {
			out[i] = reflect.Zero(outType.Out(i))
		}

		for i, o := range result.Values {
			if i >= numOut || (lastIsError && i >= numOut-1) {
				break
			}
			if o != nil {
				v := reflect.ValueOf(o)
				outType := outType.Out(i)
				if outType.Kind() == v.Kind() {
					out[i] = v
				} else {
					err = errors.New("can't unpack result")
				}
			}
		}

		if lastIsError && err != nil {
			out[len(out)-1] = reflect.ValueOf(err)
		}

		return out
	})
	outFn.Set(newFn)
	return nil
}