meta.h

00001 // Tencent is pleased to support the open source community by making RapidJSON available.
00002 // 
00003 // Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip. All rights reserved.
00004 //
00005 // Licensed under the MIT License (the "License"); you may not use this file except
00006 // in compliance with the License. You may obtain a copy of the License at
00007 //
00008 // http://opensource.org/licenses/MIT
00009 //
00010 // Unless required by applicable law or agreed to in writing, software distributed 
00011 // under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR 
00012 // CONDITIONS OF ANY KIND, either express or implied. See the License for the 
00013 // specific language governing permissions and limitations under the License.
00014 
00015 #ifndef RAPIDJSON_INTERNAL_META_H_
00016 #define RAPIDJSON_INTERNAL_META_H_
00017 
00018 #include "../rapidjson.h"
00019 
00020 #ifdef __GNUC__
00021 RAPIDJSON_DIAG_PUSH
00022 RAPIDJSON_DIAG_OFF(effc++)
00023 #endif
00024 #if defined(_MSC_VER)
00025 RAPIDJSON_DIAG_PUSH
00026 RAPIDJSON_DIAG_OFF(6334)
00027 #endif
00028 
00029 #if RAPIDJSON_HAS_CXX11_TYPETRAITS
00030 #include <type_traits>
00031 #endif
00032 
00033 //@cond RAPIDJSON_INTERNAL
00034 RAPIDJSON_NAMESPACE_BEGIN
00035 namespace internal {
00036 
00037 // Helper to wrap/convert arbitrary types to void, useful for arbitrary type matching
00038 template <typename T> struct Void { typedef void Type; };
00039 
00040 ///////////////////////////////////////////////////////////////////////////////
00041 // BoolType, TrueType, FalseType
00042 //
00043 template <bool Cond> struct BoolType {
00044     static const bool Value = Cond;
00045     typedef BoolType Type;
00046 };
00047 typedef BoolType<true> TrueType;
00048 typedef BoolType<false> FalseType;
00049 
00050 
00051 ///////////////////////////////////////////////////////////////////////////////
00052 // SelectIf, BoolExpr, NotExpr, AndExpr, OrExpr
00053 //
00054 
00055 template <bool C> struct SelectIfImpl { template <typename T1, typename T2> struct Apply { typedef T1 Type; }; };
00056 template <> struct SelectIfImpl<false> { template <typename T1, typename T2> struct Apply { typedef T2 Type; }; };
00057 template <bool C, typename T1, typename T2> struct SelectIfCond : SelectIfImpl<C>::template Apply<T1,T2> {};
00058 template <typename C, typename T1, typename T2> struct SelectIf : SelectIfCond<C::Value, T1, T2> {};
00059 
00060 template <bool Cond1, bool Cond2> struct AndExprCond : FalseType {};
00061 template <> struct AndExprCond<true, true> : TrueType {};
00062 template <bool Cond1, bool Cond2> struct OrExprCond : TrueType {};
00063 template <> struct OrExprCond<false, false> : FalseType {};
00064 
00065 template <typename C> struct BoolExpr : SelectIf<C,TrueType,FalseType>::Type {};
00066 template <typename C> struct NotExpr  : SelectIf<C,FalseType,TrueType>::Type {};
00067 template <typename C1, typename C2> struct AndExpr : AndExprCond<C1::Value, C2::Value>::Type {};
00068 template <typename C1, typename C2> struct OrExpr  : OrExprCond<C1::Value, C2::Value>::Type {};
00069 
00070 
00071 ///////////////////////////////////////////////////////////////////////////////
00072 // AddConst, MaybeAddConst, RemoveConst
00073 template <typename T> struct AddConst { typedef const T Type; };
00074 template <bool Constify, typename T> struct MaybeAddConst : SelectIfCond<Constify, const T, T> {};
00075 template <typename T> struct RemoveConst { typedef T Type; };
00076 template <typename T> struct RemoveConst<const T> { typedef T Type; };
00077 
00078 
00079 ///////////////////////////////////////////////////////////////////////////////
00080 // IsSame, IsConst, IsMoreConst, IsPointer
00081 //
00082 template <typename T, typename U> struct IsSame : FalseType {};
00083 template <typename T> struct IsSame<T, T> : TrueType {};
00084 
00085 template <typename T> struct IsConst : FalseType {};
00086 template <typename T> struct IsConst<const T> : TrueType {};
00087 
00088 template <typename CT, typename T>
00089 struct IsMoreConst
00090     : AndExpr<IsSame<typename RemoveConst<CT>::Type, typename RemoveConst<T>::Type>,
00091               BoolType<IsConst<CT>::Value >= IsConst<T>::Value> >::Type {};
00092 
00093 template <typename T> struct IsPointer : FalseType {};
00094 template <typename T> struct IsPointer<T*> : TrueType {};
00095 
00096 ///////////////////////////////////////////////////////////////////////////////
00097 // IsBaseOf
00098 //
00099 #if RAPIDJSON_HAS_CXX11_TYPETRAITS
00100 
00101 template <typename B, typename D> struct IsBaseOf
00102     : BoolType< ::std::is_base_of<B,D>::value> {};
00103 
00104 #else // simplified version adopted from Boost
00105 
00106 template<typename B, typename D> struct IsBaseOfImpl {
00107     RAPIDJSON_STATIC_ASSERT(sizeof(B) != 0);
00108     RAPIDJSON_STATIC_ASSERT(sizeof(D) != 0);
00109 
00110     typedef char (&Yes)[1];
00111     typedef char (&No) [2];
00112 
00113     template <typename T>
00114     static Yes Check(const D*, T);
00115     static No  Check(const B*, int);
00116 
00117     struct Host {
00118         operator const B*() const;
00119         operator const D*();
00120     };
00121 
00122     enum { Value = (sizeof(Check(Host(), 0)) == sizeof(Yes)) };
00123 };
00124 
00125 template <typename B, typename D> struct IsBaseOf
00126     : OrExpr<IsSame<B, D>, BoolExpr<IsBaseOfImpl<B, D> > >::Type {};
00127 
00128 #endif // RAPIDJSON_HAS_CXX11_TYPETRAITS
00129 
00130 
00131 //////////////////////////////////////////////////////////////////////////
00132 // EnableIf / DisableIf
00133 //
00134 template <bool Condition, typename T = void> struct EnableIfCond  { typedef T Type; };
00135 template <typename T> struct EnableIfCond<false, T> { /* empty */ };
00136 
00137 template <bool Condition, typename T = void> struct DisableIfCond { typedef T Type; };
00138 template <typename T> struct DisableIfCond<true, T> { /* empty */ };
00139 
00140 template <typename Condition, typename T = void>
00141 struct EnableIf : EnableIfCond<Condition::Value, T> {};
00142 
00143 template <typename Condition, typename T = void>
00144 struct DisableIf : DisableIfCond<Condition::Value, T> {};
00145 
00146 // SFINAE helpers
00147 struct SfinaeTag {};
00148 template <typename T> struct RemoveSfinaeTag;
00149 template <typename T> struct RemoveSfinaeTag<SfinaeTag&(*)(T)> { typedef T Type; };
00150 
00151 #define RAPIDJSON_REMOVEFPTR_(type) \
00152     typename ::RAPIDJSON_NAMESPACE::internal::RemoveSfinaeTag \
00153         < ::RAPIDJSON_NAMESPACE::internal::SfinaeTag&(*) type>::Type
00154 
00155 #define RAPIDJSON_ENABLEIF(cond) \
00156     typename ::RAPIDJSON_NAMESPACE::internal::EnableIf \
00157         <RAPIDJSON_REMOVEFPTR_(cond)>::Type * = NULL
00158 
00159 #define RAPIDJSON_DISABLEIF(cond) \
00160     typename ::RAPIDJSON_NAMESPACE::internal::DisableIf \
00161         <RAPIDJSON_REMOVEFPTR_(cond)>::Type * = NULL
00162 
00163 #define RAPIDJSON_ENABLEIF_RETURN(cond,returntype) \
00164     typename ::RAPIDJSON_NAMESPACE::internal::EnableIf \
00165         <RAPIDJSON_REMOVEFPTR_(cond), \
00166          RAPIDJSON_REMOVEFPTR_(returntype)>::Type
00167 
00168 #define RAPIDJSON_DISABLEIF_RETURN(cond,returntype) \
00169     typename ::RAPIDJSON_NAMESPACE::internal::DisableIf \
00170         <RAPIDJSON_REMOVEFPTR_(cond), \
00171          RAPIDJSON_REMOVEFPTR_(returntype)>::Type
00172 
00173 } // namespace internal
00174 RAPIDJSON_NAMESPACE_END
00175 //@endcond
00176 
00177 #if defined(__GNUC__) || defined(_MSC_VER)
00178 RAPIDJSON_DIAG_POP
00179 #endif
00180 
00181 #endif // RAPIDJSON_INTERNAL_META_H_