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 */ 24 template <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. */ 31 template <bool b> struct SkTBool : SkTIntegralConstant<bool, b> { }; 32 33 /** Pre-C++11 version of std::true_type. */ 34 typedef SkTBool<true> SkTrue; 35 36 /** Pre-C++11 version of std::false_type. */ 37 typedef SkTBool<false> SkFalse; 38 39 /** SkTIf_c::type = (condition) ? T : F; 40 * Pre-C++11 version of std::conditional. 41 */ 42 template <bool condition, typename T, typename F> struct SkTIf_c { 43 typedef F type; 44 }; 45 template <typename T, typename F> struct SkTIf_c<true, T, F> { 46 typedef T type; 47 }; 48 49 /** SkTIf::type = (Condition::value) ? T : F; */ 50 template <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; */ 55 template <typename a, typename b, typename Both, typename A, typename B, typename Neither> 56 struct 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
