appengine.go

package cachestore

// This file contains code copied from appengine.datastore for memcache key generation for the -multi methods.

import (
	"reflect"

	"appengine/datastore"
)

const (
	multiArgTypeInvalid multiArgType = iota
	multiArgTypePropertyLoadSaver
	multiArgTypeStruct
	multiArgTypeStructPtr
	multiArgTypeInterface
)

type multiArgType int

var (
	typeOfPropertyLoadSaver = reflect.TypeOf((*datastore.PropertyLoadSaver)(nil)).Elem()
	typeOfPropertyList      = reflect.TypeOf(datastore.PropertyList(nil))
)

// checkMultiArg checks that v has type []S, []*S, []I, or []P, for some struct
// type S, for some interface type I, or some non-interface non-pointer type P
// such that P or *P implements PropertyLoadSaver.
//
// It returns what category the slice's elements are, and the reflect.Type
// that represents S, I or P.
//
// As a special case, PropertyList is an invalid type for v.
func checkMultiArg(v reflect.Value) (m multiArgType, elemType reflect.Type) {
	if v.Kind() != reflect.Slice {
		return multiArgTypeInvalid, nil
	}
	if v.Type() == typeOfPropertyList {
		return multiArgTypeInvalid, nil
	}
	elemType = v.Type().Elem()
	if reflect.PtrTo(elemType).Implements(typeOfPropertyLoadSaver) {
		return multiArgTypePropertyLoadSaver, elemType
	}
	switch elemType.Kind() {
	case reflect.Struct:
		return multiArgTypeStruct, elemType
	case reflect.Interface:
		return multiArgTypeInterface, elemType
	case reflect.Ptr:
		elemType = elemType.Elem()
		if elemType.Kind() == reflect.Struct {
			return multiArgTypeStructPtr, elemType
		}
	}
	return multiArgTypeInvalid, nil
}