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internal/meta.h: add some template meta functions

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* Add/RemoveConst
 * IsSame, IsConst, IsMoreConst
 * Enable/DisableIf (including helper macro)
This commit is contained in:
Philipp A. Hartmann 2014-07-03 14:24:58 +02:00
parent 0bce2dedd2
commit 05179e2891
1 changed files with 71 additions and 0 deletions
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include/rapidjson/internal/meta.h Normal file
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#ifndef RAPIDJSON_INTERNAL_META_H_
#define RAPIDJSON_INTERNAL_META_H_
//@cond RAPIDJSON_INTERNAL
namespace rapidjson {
namespace internal {
template <int N> struct IntegralC { enum { Value = N }; };
template <bool Cond> struct BoolType : IntegralC<Cond> {};
struct TrueType : BoolType<true> {};
struct FalseType : BoolType<false> {};
template <typename T> struct AddConst { typedef const T Type; };
template <typename T> struct RemoveConst { typedef T Type; };
template <typename T> struct RemoveConst<const T> { typedef T Type; };
template <bool Condition, typename T1, typename T2> struct SelectIfCond;
template <typename T1, typename T2> struct SelectIfCond<true,T1,T2> { typedef T1 Type; };
template <typename T1, typename T2> struct SelectIfCond<false,T1,T2> { typedef T2 Type; };
template <typename Condition, typename T1, typename T2>
struct SelectIf : SelectIfCond<Condition::Value,T1,T2> {};
template <bool Constify, typename T>
struct MaybeAddConst : SelectIfCond<Constify, const T, T> {};
template <typename T, typename U> struct IsSame { enum { Value = false }; };
template <typename T> struct IsSame<T,T> { enum { Value = true }; };
template <typename T> struct IsConst { enum { Value = false }; };
template <typename T> struct IsConst<const T> { enum { Value = true }; };
template <typename CT, typename T>
struct IsMoreConst {
enum { Value =
( IsSame< typename RemoveConst<CT>::Type, typename RemoveConst<T>::Type>::Value
&& ( IsConst<CT>::Value >= IsConst<T>::Value ) )
};
};
template <bool Condition, typename T = void> struct EnableIfCond;
template <typename T> struct EnableIfCond<true, T> { typedef T Type; };
template <typename T> struct EnableIfCond<false, T> { /* empty */ };
template <bool Condition, typename T = void>
struct DisableIfCond : EnableIfCond<not Condition, T> {};
template <typename Condition, typename T = void>
struct EnableIf : EnableIfCond<Condition::Value, T> {};
template <typename Condition, typename T = void>
struct DisableIf : DisableIfCond<Condition::Value, T> {};
// SFINAE helpers
struct SfinaeResultTag {};
template <typename T> struct RemoveSfinaeFptr {};
template <typename T> struct RemoveSfinaeFptr<SfinaeResultTag&(*)(T)> { typedef T Type; };
#define RAPIDJSON_REMOVEFPTR_(type) \
typename ::rapidjson::internal::RemoveSfinaeFptr \
< ::rapidjson::internal::SfinaeResultTag&(*) type>::Type
#define RAPIDJSON_ENABLEIF(cond) \
typename ::rapidjson::internal::EnableIf \
<RAPIDJSON_REMOVEFPTR_(cond)>::Type * = NULL
} // namespace internal
} // namespace rapidjson
//@endcond
#endif // RAPIDJSON_INTERNAL_META_H_