1/*
2 * Copyright 2013 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 *
7 *
8 * This header provides some of the helpers (std::integral_constant) and
9 * type transformations (std::conditional) which will become available with
10 * C++11 in the type_traits header.
11 *
12 * Because we lack constexpr, we cannot mimic
13 * std::integral_constant::'constexpr operator T()'.
14 * As a result we introduce SkTBool and SkTIf similar to Boost in order to
15 * minimize the visual noise of many uses of '::value'.
16 */
17
18#ifndef SkTLogic_DEFINED
19#define SkTLogic_DEFINED
20
21/** Represents a templated integer constant.
22 *  Pre-C++11 version of std::integral_constant.
23 */
24template <typename T, T v> struct SkTIntegralConstant {
25    static const T value = v;
26    typedef T value_type;
27    typedef SkTIntegralConstant<T, v> type;
28};
29
30/** Convenience specialization of SkTIntegralConstant. */
31template <bool b> struct SkTBool : SkTIntegralConstant<bool, b> { };
32
33/** Pre-C++11 version of std::true_type. */
34typedef SkTBool<true> SkTrue;
35
36/** Pre-C++11 version of std::false_type. */
37typedef SkTBool<false> SkFalse;
38
39/** SkTIf_c::type = (condition) ? T : F;
40 *  Pre-C++11 version of std::conditional.
41 */
42template <bool condition, typename T, typename F> struct SkTIf_c {
43    typedef F type;
44};
45template <typename T, typename F> struct SkTIf_c<true, T, F> {
46    typedef T type;
47};
48
49/** SkTIf::type = (Condition::value) ? T : F; */
50template <typename Condition, typename T, typename F> struct SkTIf {
51    typedef typename SkTIf_c<static_cast<bool>(Condition::value), T, F>::type type;
52};
53
54/** SkTMux::type = (a && b) ? Both : (a) ? A : (b) ? B : Neither; */
55template <typename a, typename b, typename Both, typename A, typename B, typename Neither>
56struct SkTMux {
57    typedef typename SkTIf<a, typename SkTIf<b, Both, A>::type,
58                              typename SkTIf<b, B, Neither>::type>::type type;
59};
60
61#endif
62