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meta.h: simplify meta programming helpers

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Some (older) compilers have problems with compile-time constants.
This commit simplifies the implementation of the helper classes
in order to improve compiler support, especially be removing the
need of partial template specialisation.

No functional changes.
This commit is contained in:
Philipp A. Hartmann 2014-08-30 13:10:56 +02:00
parent b56641106b
commit ed282b8141
1 changed files with 53 additions and 29 deletions
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82
include/rapidjson/internal/meta.h
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@ -30,51 +30,75 @@ RAPIDJSON_DIAG_OFF(effc++)
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> {};
///////////////////////////////////////////////////////////////////////////////
// BoolType, TrueType, FalseType
//
template <bool Cond> struct BoolType {
static const bool Value = Cond;
typedef BoolType Type;
};
typedef BoolType<true> TrueType;
typedef BoolType<false> FalseType;
///////////////////////////////////////////////////////////////////////////////
// SelectIf, BoolExpr, NotExpr, AndExpr, OrExpr
//
template <bool C> struct SelectIfImpl { template <typename T1, typename T2> struct Apply { typedef T1 Type; }; };
template <> struct SelectIfImpl<false> { template <typename T1, typename T2> struct Apply { typedef T2 Type; }; };
template <bool C, typename T1, typename T2> struct SelectIfCond : SelectIfImpl<C>::template Apply<T1,T2> {};
template <typename C, typename T1, typename T2> struct SelectIf : SelectIfCond<C::Value, T1, T2> {};
template <bool Cond1, bool Cond2> struct AndExprCond : FalseType {};
template <> struct AndExprCond<true, true> : TrueType {};
template <bool Cond1, bool Cond2> struct OrExprCond : TrueType {};
template <> struct OrExprCond<false, false> : FalseType {};
template <typename C> struct BoolExpr : SelectIf<C,TrueType,FalseType>::Type {};
template <typename C> struct NotExpr : SelectIf<C,FalseType,TrueType>::Type {};
template <typename C1, typename C2> struct AndExpr : AndExprCond<C1::Value, C2::Value>::Type {};
template <typename C1, typename C2> struct OrExpr : OrExprCond<C1::Value, C2::Value>::Type {};
///////////////////////////////////////////////////////////////////////////////
// AddConst, MaybeAddConst, RemoveConst
template <typename T> struct AddConst { typedef const T Type; };
template <bool Constify, typename T> struct MaybeAddConst : SelectIfCond<Constify, const T, T> {};
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 : FalseType {};
template <typename T> struct IsSame<T,T> : TrueType {};
///////////////////////////////////////////////////////////////////////////////
// IsSame, IsConst, IsMoreConst, IsPointer
//
template <typename T, typename U> struct IsSame : FalseType {};
template <typename T> struct IsSame<T, T> : TrueType {};
template <typename T> struct IsConst : FalseType {};
template <typename T> struct IsConst<const T> : TrueType {};
template <typename CT, typename T>
struct IsMoreConst
: AndExpr<IsSame<typename RemoveConst<CT>::Type, typename RemoveConst<T>::Type>,
BoolType<IsConst<CT>::Value >= IsConst<T>::Value> >::Type {};
template <typename T> struct IsPointer : FalseType {};
template <typename T> struct IsPointer<T*> : TrueType {};
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 ) )
};
};
//////////////////////////////////////////////////////////////////////////
// EnableIf / DisableIf
//
template <bool Condition, typename T = void> struct EnableIfCond;
template <typename T> struct EnableIfCond<true, T> { typedef T Type; };
template <bool Condition, typename T = void> struct EnableIfCond { typedef T Type; };
template <typename T> struct EnableIfCond<false, T> { /* empty */ };
template <bool Condition, typename T = void>
struct DisableIfCond : EnableIfCond<!Condition, T> {};
template <bool Condition, typename T = void> struct DisableIfCond { typedef T Type; };
template <typename T> struct DisableIfCond<true, T> { /* empty */ };
template <typename Condition, typename T = void>
struct EnableIf : EnableIfCond<Condition::Value, T> {};
@ -83,13 +107,13 @@ 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; };
struct SfinaeTag {};
template <typename T> struct RemoveSfinaeTag;
template <typename T> struct RemoveSfinaeTag<SfinaeTag&(*)(T)> { typedef T Type; };
#define RAPIDJSON_REMOVEFPTR_(type) \
typename ::rapidjson::internal::RemoveSfinaeFptr \
< ::rapidjson::internal::SfinaeResultTag&(*) type>::Type
typename ::rapidjson::internal::RemoveSfinaeTag \
< ::rapidjson::internal::SfinaeTag&(*) type>::Type
#define RAPIDJSON_ENABLEIF(cond) \
typename ::rapidjson::internal::EnableIf \