/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */ /* vim: set ts=8 sts=2 et sw=2 tw=80: */ /* This Source Code Form is subject to the terms of the Mozilla Public * License, v. 2.0. If a copy of the MPL was not distributed with this * file, You can obtain one at http://mozilla.org/MPL/2.0/. */ /* Template-based metaprogramming and type-testing facilities. */ #ifndef mozilla_TypeTraits_h #define mozilla_TypeTraits_h #include "mozilla/Types.h" /* * These traits are approximate copies of the traits and semantics from C++11's * <type_traits> header. Don't add traits not in that header! When all * platforms provide that header, we can convert all users and remove this one. */ #include <wchar.h> namespace mozilla { /* Forward declarations. */ template<typename> struct RemoveCV; template<typename> struct AddRvalueReference; /* 20.2.4 Function template declval [declval] */ /** * DeclVal simplifies the definition of expressions which occur as unevaluated * operands. It converts T to a reference type, making it possible to use in * decltype expressions even if T does not have a default constructor, e.g.: * decltype(DeclVal<TWithNoDefaultConstructor>().foo()) */ template<typename T> typename AddRvalueReference<T>::Type DeclVal(); /* 20.9.3 Helper classes [meta.help] */ /** * Helper class used as a base for various type traits, exposed publicly * because <type_traits> exposes it as well. */ template<typename T, T Value> struct IntegralConstant { static const T value = Value; typedef T ValueType; typedef IntegralConstant<T, Value> Type; }; /** Convenient aliases. */ typedef IntegralConstant<bool, true> TrueType; typedef IntegralConstant<bool, false> FalseType; /* 20.9.4 Unary type traits [meta.unary] */ /* 20.9.4.1 Primary type categories [meta.unary.cat] */ namespace detail { template<typename T> struct IsVoidHelper : FalseType {}; template<> struct IsVoidHelper<void> : TrueType {}; } // namespace detail /** * IsVoid determines whether a type is void. * * mozilla::IsVoid<int>::value is false; * mozilla::IsVoid<void>::value is true; * mozilla::IsVoid<void*>::value is false; * mozilla::IsVoid<volatile void>::value is true. */ template<typename T> struct IsVoid : detail::IsVoidHelper<typename RemoveCV<T>::Type> {}; namespace detail { template <typename T> struct IsIntegralHelper : FalseType {}; template<> struct IsIntegralHelper<char> : TrueType {}; template<> struct IsIntegralHelper<signed char> : TrueType {}; template<> struct IsIntegralHelper<unsigned char> : TrueType {}; template<> struct IsIntegralHelper<short> : TrueType {}; template<> struct IsIntegralHelper<unsigned short> : TrueType {}; template<> struct IsIntegralHelper<int> : TrueType {}; template<> struct IsIntegralHelper<unsigned int> : TrueType {}; template<> struct IsIntegralHelper<long> : TrueType {}; template<> struct IsIntegralHelper<unsigned long> : TrueType {}; template<> struct IsIntegralHelper<long long> : TrueType {}; template<> struct IsIntegralHelper<unsigned long long> : TrueType {}; template<> struct IsIntegralHelper<bool> : TrueType {}; template<> struct IsIntegralHelper<wchar_t> : TrueType {}; template<> struct IsIntegralHelper<char16_t> : TrueType {}; } /* namespace detail */ /** * IsIntegral determines whether a type is an integral type. * * mozilla::IsIntegral<int>::value is true; * mozilla::IsIntegral<unsigned short>::value is true; * mozilla::IsIntegral<const long>::value is true; * mozilla::IsIntegral<int*>::value is false; * mozilla::IsIntegral<double>::value is false; */ template<typename T> struct IsIntegral : detail::IsIntegralHelper<typename RemoveCV<T>::Type> {}; template<typename T, typename U> struct IsSame; namespace detail { template<typename T> struct IsFloatingPointHelper : IntegralConstant<bool, IsSame<T, float>::value || IsSame<T, double>::value || IsSame<T, long double>::value> {}; } // namespace detail /** * IsFloatingPoint determines whether a type is a floating point type (float, * double, long double). * * mozilla::IsFloatingPoint<int>::value is false; * mozilla::IsFloatingPoint<const float>::value is true; * mozilla::IsFloatingPoint<long double>::value is true; * mozilla::IsFloatingPoint<double*>::value is false. */ template<typename T> struct IsFloatingPoint : detail::IsFloatingPointHelper<typename RemoveCV<T>::Type> {}; namespace detail { template<typename T> struct IsArrayHelper : FalseType {}; template<typename T, decltype(sizeof(1)) N> struct IsArrayHelper<T[N]> : TrueType {}; template<typename T> struct IsArrayHelper<T[]> : TrueType {}; } // namespace detail /** * IsArray determines whether a type is an array type, of known or unknown * length. * * mozilla::IsArray<int>::value is false; * mozilla::IsArray<int[]>::value is true; * mozilla::IsArray<int[5]>::value is true. */ template<typename T> struct IsArray : detail::IsArrayHelper<typename RemoveCV<T>::Type> {}; namespace detail { template<typename T> struct IsFunPtr; template<typename> struct IsFunPtr : public FalseType {}; template<typename Result, typename... ArgTypes> struct IsFunPtr<Result(*)(ArgTypes...)> : public TrueType {}; }; // namespace detail /** * IsFunction determines whether a type is a function type. Function pointers * don't qualify here--only the type of an actual function symbol. We do not * correctly handle varags function types because of a bug in MSVC. * * Given the function: * void f(int) {} * * mozilla::IsFunction<void(int)> is true; * mozilla::IsFunction<void(*)(int)> is false; * mozilla::IsFunction<decltype(f)> is true. */ template<typename T> struct IsFunction : public detail::IsFunPtr<typename RemoveCV<T>::Type *> {}; namespace detail { template<typename T> struct IsPointerHelper : FalseType {}; template<typename T> struct IsPointerHelper<T*> : TrueType {}; } // namespace detail /** * IsPointer determines whether a type is a possibly-CV-qualified pointer type * (but not a pointer-to-member type). * * mozilla::IsPointer<struct S*>::value is true; * mozilla::IsPointer<int*>::value is true; * mozilla::IsPointer<int**>::value is true; * mozilla::IsPointer<const int*>::value is true; * mozilla::IsPointer<int* const>::value is true; * mozilla::IsPointer<int* volatile>::value is true; * mozilla::IsPointer<void (*)(void)>::value is true; * mozilla::IsPointer<int>::value is false; * mozilla::IsPointer<struct S>::value is false. * mozilla::IsPointer<int(struct S::*)>::value is false */ template<typename T> struct IsPointer : detail::IsPointerHelper<typename RemoveCV<T>::Type> {}; /** * IsLvalueReference determines whether a type is an lvalue reference. * * mozilla::IsLvalueReference<struct S*>::value is false; * mozilla::IsLvalueReference<int**>::value is false; * mozilla::IsLvalueReference<void (*)(void)>::value is false; * mozilla::IsLvalueReference<int>::value is false; * mozilla::IsLvalueReference<struct S>::value is false; * mozilla::IsLvalueReference<struct S*&>::value is true; * mozilla::IsLvalueReference<struct S&&>::value is false. */ template<typename T> struct IsLvalueReference : FalseType {}; template<typename T> struct IsLvalueReference<T&> : TrueType {}; /** * IsRvalueReference determines whether a type is an rvalue reference. * * mozilla::IsRvalueReference<struct S*>::value is false; * mozilla::IsRvalueReference<int**>::value is false; * mozilla::IsRvalueReference<void (*)(void)>::value is false; * mozilla::IsRvalueReference<int>::value is false; * mozilla::IsRvalueReference<struct S>::value is false; * mozilla::IsRvalueReference<struct S*&>::value is false; * mozilla::IsRvalueReference<struct S&&>::value is true. */ template<typename T> struct IsRvalueReference : FalseType {}; template<typename T> struct IsRvalueReference<T&&> : TrueType {}; namespace detail { // __is_enum is a supported extension across all of our supported compilers. template<typename T> struct IsEnumHelper : IntegralConstant<bool, __is_enum(T)> {}; } // namespace detail /** * IsEnum determines whether a type is an enum type. * * mozilla::IsEnum<enum S>::value is true; * mozilla::IsEnum<enum S*>::value is false; * mozilla::IsEnum<int>::value is false; */ template<typename T> struct IsEnum : detail::IsEnumHelper<typename RemoveCV<T>::Type> {}; namespace detail { // __is_class is a supported extension across all of our supported compilers: // http://llvm.org/releases/3.0/docs/ClangReleaseNotes.html // http://gcc.gnu.org/onlinedocs/gcc-4.4.7/gcc/Type-Traits.html#Type-Traits // http://msdn.microsoft.com/en-us/library/ms177194%28v=vs.100%29.aspx template<typename T> struct IsClassHelper : IntegralConstant<bool, __is_class(T)> {}; } // namespace detail /** * IsClass determines whether a type is a class type (but not a union). * * struct S {}; * union U {}; * mozilla::IsClass<int>::value is false; * mozilla::IsClass<const S>::value is true; * mozilla::IsClass<U>::value is false; */ template<typename T> struct IsClass : detail::IsClassHelper<typename RemoveCV<T>::Type> {}; /* 20.9.4.2 Composite type traits [meta.unary.comp] */ /** * IsReference determines whether a type is an lvalue or rvalue reference. * * mozilla::IsReference<struct S*>::value is false; * mozilla::IsReference<int**>::value is false; * mozilla::IsReference<int&>::value is true; * mozilla::IsReference<void (*)(void)>::value is false; * mozilla::IsReference<const int&>::value is true; * mozilla::IsReference<int>::value is false; * mozilla::IsReference<struct S>::value is false; * mozilla::IsReference<struct S&>::value is true; * mozilla::IsReference<struct S*&>::value is true; * mozilla::IsReference<struct S&&>::value is true. */ template<typename T> struct IsReference : IntegralConstant<bool, IsLvalueReference<T>::value || IsRvalueReference<T>::value> {}; /** * IsArithmetic determines whether a type is arithmetic. A type is arithmetic * iff it is an integral type or a floating point type. * * mozilla::IsArithmetic<int>::value is true; * mozilla::IsArithmetic<double>::value is true; * mozilla::IsArithmetic<long double*>::value is false. */ template<typename T> struct IsArithmetic : IntegralConstant<bool, IsIntegral<T>::value || IsFloatingPoint<T>::value> {}; namespace detail { template<typename T> struct IsMemberPointerHelper : FalseType {}; template<typename T, typename U> struct IsMemberPointerHelper<T U::*> : TrueType {}; } // namespace detail /** * IsMemberPointer determines whether a type is pointer to non-static member * object or a pointer to non-static member function. * * mozilla::IsMemberPointer<int(cls::*)>::value is true * mozilla::IsMemberPointer<int*>::value is false */ template<typename T> struct IsMemberPointer : detail::IsMemberPointerHelper<typename RemoveCV<T>::Type> {}; /** * IsScalar determines whether a type is a scalar type. * * mozilla::IsScalar<int>::value is true * mozilla::IsScalar<int*>::value is true * mozilla::IsScalar<cls>::value is false */ template<typename T> struct IsScalar : IntegralConstant<bool, IsArithmetic<T>::value || IsEnum<T>::value || IsPointer<T>::value || IsMemberPointer<T>::value> {}; /* 20.9.4.3 Type properties [meta.unary.prop] */ /** * IsConst determines whether a type is const or not. * * mozilla::IsConst<int>::value is false; * mozilla::IsConst<void* const>::value is true; * mozilla::IsConst<const char*>::value is false. */ template<typename T> struct IsConst : FalseType {}; template<typename T> struct IsConst<const T> : TrueType {}; /** * IsVolatile determines whether a type is volatile or not. * * mozilla::IsVolatile<int>::value is false; * mozilla::IsVolatile<void* volatile>::value is true; * mozilla::IsVolatile<volatile char*>::value is false. */ template<typename T> struct IsVolatile : FalseType {}; template<typename T> struct IsVolatile<volatile T> : TrueType {}; /** * Traits class for identifying POD types. Until C++11 there's no automatic * way to detect PODs, so for the moment this is done manually. Users may * define specializations of this class that inherit from mozilla::TrueType and * mozilla::FalseType (or equivalently mozilla::IntegralConstant<bool, true or * false>, or conveniently from mozilla::IsPod for composite types) as needed to * ensure correct IsPod behavior. */ template<typename T> struct IsPod : public FalseType {}; template<> struct IsPod<char> : TrueType {}; template<> struct IsPod<signed char> : TrueType {}; template<> struct IsPod<unsigned char> : TrueType {}; template<> struct IsPod<short> : TrueType {}; template<> struct IsPod<unsigned short> : TrueType {}; template<> struct IsPod<int> : TrueType {}; template<> struct IsPod<unsigned int> : TrueType {}; template<> struct IsPod<long> : TrueType {}; template<> struct IsPod<unsigned long> : TrueType {}; template<> struct IsPod<long long> : TrueType {}; template<> struct IsPod<unsigned long long> : TrueType {}; template<> struct IsPod<bool> : TrueType {}; template<> struct IsPod<float> : TrueType {}; template<> struct IsPod<double> : TrueType {}; template<> struct IsPod<wchar_t> : TrueType {}; template<> struct IsPod<char16_t> : TrueType {}; template<typename T> struct IsPod<T*> : TrueType {}; namespace detail { // __is_empty is a supported extension across all of our supported compilers: // http://llvm.org/releases/3.0/docs/ClangReleaseNotes.html // http://gcc.gnu.org/onlinedocs/gcc-4.4.7/gcc/Type-Traits.html#Type-Traits // http://msdn.microsoft.com/en-us/library/ms177194%28v=vs.100%29.aspx template<typename T> struct IsEmptyHelper : IntegralConstant<bool, IsClass<T>::value && __is_empty(T)> {}; } // namespace detail /** * IsEmpty determines whether a type is a class (but not a union) that is empty. * * A class is empty iff it and all its base classes have no non-static data * members (except bit-fields of length 0) and no virtual member functions, and * no base class is empty or a virtual base class. * * Intuitively, empty classes don't have any data that has to be stored in * instances of those classes. (The size of the class must still be non-zero, * because distinct array elements of any type must have different addresses. * However, if the Empty Base Optimization is implemented by the compiler [most * compilers implement it, and in certain cases C++11 requires it], the size of * a class inheriting from an empty |Base| class need not be inflated by * |sizeof(Base)|.) And intuitively, non-empty classes have data members and/or * vtable pointers that must be stored in each instance for proper behavior. * * static_assert(!mozilla::IsEmpty<int>::value, "not a class => not empty"); * union U1 { int x; }; * static_assert(!mozilla::IsEmpty<U1>::value, "not a class => not empty"); * struct E1 {}; * struct E2 { int : 0 }; * struct E3 : E1 {}; * struct E4 : E2 {}; * static_assert(mozilla::IsEmpty<E1>::value && * mozilla::IsEmpty<E2>::value && * mozilla::IsEmpty<E3>::value && * mozilla::IsEmpty<E4>::value, * "all empty"); * union U2 { E1 e1; }; * static_assert(!mozilla::IsEmpty<U2>::value, "not a class => not empty"); * struct NE1 { int x; }; * struct NE2 : virtual E1 {}; * struct NE3 : E2 { virtual ~NE3() {} }; * struct NE4 { virtual void f() {} }; * static_assert(!mozilla::IsEmpty<NE1>::value && * !mozilla::IsEmpty<NE2>::value && * !mozilla::IsEmpty<NE3>::value && * !mozilla::IsEmpty<NE4>::value, * "all empty"); */ template<typename T> struct IsEmpty : detail::IsEmptyHelper<typename RemoveCV<T>::Type> {}; namespace detail { template<typename T, bool = IsFloatingPoint<T>::value, bool = IsIntegral<T>::value, typename NoCV = typename RemoveCV<T>::Type> struct IsSignedHelper; // Floating point is signed. template<typename T, typename NoCV> struct IsSignedHelper<T, true, false, NoCV> : TrueType {}; // Integral is conditionally signed. template<typename T, typename NoCV> struct IsSignedHelper<T, false, true, NoCV> : IntegralConstant<bool, bool(NoCV(-1) < NoCV(1))> {}; // Non-floating point, non-integral is not signed. template<typename T, typename NoCV> struct IsSignedHelper<T, false, false, NoCV> : FalseType {}; } // namespace detail /** * IsSigned determines whether a type is a signed arithmetic type. |char| is * considered a signed type if it has the same representation as |signed char|. * * mozilla::IsSigned<int>::value is true; * mozilla::IsSigned<const unsigned int>::value is false; * mozilla::IsSigned<unsigned char>::value is false; * mozilla::IsSigned<float>::value is true. */ template<typename T> struct IsSigned : detail::IsSignedHelper<T> {}; namespace detail { template<typename T, bool = IsFloatingPoint<T>::value, bool = IsIntegral<T>::value, typename NoCV = typename RemoveCV<T>::Type> struct IsUnsignedHelper; // Floating point is not unsigned. template<typename T, typename NoCV> struct IsUnsignedHelper<T, true, false, NoCV> : FalseType {}; // Integral is conditionally unsigned. template<typename T, typename NoCV> struct IsUnsignedHelper<T, false, true, NoCV> : IntegralConstant<bool, (IsSame<NoCV, bool>::value || bool(NoCV(1) < NoCV(-1)))> {}; // Non-floating point, non-integral is not unsigned. template<typename T, typename NoCV> struct IsUnsignedHelper<T, false, false, NoCV> : FalseType {}; } // namespace detail /** * IsUnsigned determines whether a type is an unsigned arithmetic type. * * mozilla::IsUnsigned<int>::value is false; * mozilla::IsUnsigned<const unsigned int>::value is true; * mozilla::IsUnsigned<unsigned char>::value is true; * mozilla::IsUnsigned<float>::value is false. */ template<typename T> struct IsUnsigned : detail::IsUnsignedHelper<T> {}; namespace detail { struct DoIsDestructibleImpl { template<typename T, typename = decltype(DeclVal<T&>().~T())> static TrueType test(int); template<typename T> static FalseType test(...); }; template<typename T> struct IsDestructibleImpl : public DoIsDestructibleImpl { typedef decltype(test<T>(0)) Type; }; } // namespace detail template<typename T> struct IsDestructible : public detail::IsDestructibleImpl<T>::Type {}; /* 20.9.5 Type property queries [meta.unary.prop.query] */ /* 20.9.6 Relationships between types [meta.rel] */ /** * IsSame tests whether two types are the same type. * * mozilla::IsSame<int, int>::value is true; * mozilla::IsSame<int*, int*>::value is true; * mozilla::IsSame<int, unsigned int>::value is false; * mozilla::IsSame<void, void>::value is true; * mozilla::IsSame<const int, int>::value is false; * mozilla::IsSame<struct S, struct S>::value is true. */ template<typename T, typename U> struct IsSame : FalseType {}; template<typename T> struct IsSame<T, T> : TrueType {}; namespace detail { #if defined(__GNUC__) || defined(__clang__) || defined(_MSC_VER) template<class Base, class Derived> struct BaseOfTester : IntegralConstant<bool, __is_base_of(Base, Derived)> {}; #else // The trickery used to implement IsBaseOf here makes it possible to use it for // the cases of private and multiple inheritance. This code was inspired by the // sample code here: // // http://stackoverflow.com/questions/2910979/how-is-base-of-works template<class Base, class Derived> struct BaseOfHelper { public: operator Base*() const; operator Derived*(); }; template<class Base, class Derived> struct BaseOfTester { private: template<class T> static char test(Derived*, T); static int test(Base*, int); public: static const bool value = sizeof(test(BaseOfHelper<Base, Derived>(), int())) == sizeof(char); }; template<class Base, class Derived> struct BaseOfTester<Base, const Derived> { private: template<class T> static char test(Derived*, T); static int test(Base*, int); public: static const bool value = sizeof(test(BaseOfHelper<Base, Derived>(), int())) == sizeof(char); }; template<class Base, class Derived> struct BaseOfTester<Base&, Derived&> : FalseType {}; template<class Type> struct BaseOfTester<Type, Type> : TrueType {}; template<class Type> struct BaseOfTester<Type, const Type> : TrueType {}; #endif } /* namespace detail */ /* * IsBaseOf allows to know whether a given class is derived from another. * * Consider the following class definitions: * * class A {}; * class B : public A {}; * class C {}; * * mozilla::IsBaseOf<A, B>::value is true; * mozilla::IsBaseOf<A, C>::value is false; */ template<class Base, class Derived> struct IsBaseOf : IntegralConstant<bool, detail::BaseOfTester<Base, Derived>::value> {}; namespace detail { template<typename From, typename To> struct ConvertibleTester { private: template<typename To1> static char test_helper(To1); template<typename From1, typename To1> static decltype(test_helper<To1>(DeclVal<From1>())) test(int); template<typename From1, typename To1> static int test(...); public: static const bool value = sizeof(test<From, To>(0)) == sizeof(char); }; } // namespace detail /** * IsConvertible determines whether a value of type From will implicitly convert * to a value of type To. For example: * * struct A {}; * struct B : public A {}; * struct C {}; * * mozilla::IsConvertible<A, A>::value is true; * mozilla::IsConvertible<A*, A*>::value is true; * mozilla::IsConvertible<B, A>::value is true; * mozilla::IsConvertible<B*, A*>::value is true; * mozilla::IsConvertible<C, A>::value is false; * mozilla::IsConvertible<A, C>::value is false; * mozilla::IsConvertible<A*, C*>::value is false; * mozilla::IsConvertible<C*, A*>::value is false. * * For obscure reasons, you can't use IsConvertible when the types being tested * are related through private inheritance, and you'll get a compile error if * you try. Just don't do it! * * Note - we need special handling for void, which ConvertibleTester doesn't * handle. The void handling here doesn't handle const/volatile void correctly, * which could be easily fixed if the need arises. */ template<typename From, typename To> struct IsConvertible : IntegralConstant<bool, detail::ConvertibleTester<From, To>::value> {}; template<typename B> struct IsConvertible<void, B> : IntegralConstant<bool, IsVoid<B>::value> {}; template<typename A> struct IsConvertible<A, void> : IntegralConstant<bool, IsVoid<A>::value> {}; template<> struct IsConvertible<void, void> : TrueType {}; /* 20.9.7 Transformations between types [meta.trans] */ /* 20.9.7.1 Const-volatile modifications [meta.trans.cv] */ /** * RemoveConst removes top-level const qualifications on a type. * * mozilla::RemoveConst<int>::Type is int; * mozilla::RemoveConst<const int>::Type is int; * mozilla::RemoveConst<const int*>::Type is const int*; * mozilla::RemoveConst<int* const>::Type is int*. */ template<typename T> struct RemoveConst { typedef T Type; }; template<typename T> struct RemoveConst<const T> { typedef T Type; }; /** * RemoveVolatile removes top-level volatile qualifications on a type. * * mozilla::RemoveVolatile<int>::Type is int; * mozilla::RemoveVolatile<volatile int>::Type is int; * mozilla::RemoveVolatile<volatile int*>::Type is volatile int*; * mozilla::RemoveVolatile<int* volatile>::Type is int*. */ template<typename T> struct RemoveVolatile { typedef T Type; }; template<typename T> struct RemoveVolatile<volatile T> { typedef T Type; }; /** * RemoveCV removes top-level const and volatile qualifications on a type. * * mozilla::RemoveCV<int>::Type is int; * mozilla::RemoveCV<const int>::Type is int; * mozilla::RemoveCV<volatile int>::Type is int; * mozilla::RemoveCV<int* const volatile>::Type is int*. */ template<typename T> struct RemoveCV { typedef typename RemoveConst<typename RemoveVolatile<T>::Type>::Type Type; }; /* 20.9.7.2 Reference modifications [meta.trans.ref] */ /** * Converts reference types to the underlying types. * * mozilla::RemoveReference<T>::Type is T; * mozilla::RemoveReference<T&>::Type is T; * mozilla::RemoveReference<T&&>::Type is T; */ template<typename T> struct RemoveReference { typedef T Type; }; template<typename T> struct RemoveReference<T&> { typedef T Type; }; template<typename T> struct RemoveReference<T&&> { typedef T Type; }; template<bool Condition, typename A, typename B> struct Conditional; namespace detail { enum Voidness { TIsVoid, TIsNotVoid }; template<typename T, Voidness V = IsVoid<T>::value ? TIsVoid : TIsNotVoid> struct AddLvalueReferenceHelper; template<typename T> struct AddLvalueReferenceHelper<T, TIsVoid> { typedef void Type; }; template<typename T> struct AddLvalueReferenceHelper<T, TIsNotVoid> { typedef T& Type; }; } // namespace detail /** * AddLvalueReference adds an lvalue & reference to T if one isn't already * present. (Note: adding an lvalue reference to an rvalue && reference in * essence replaces the && with a &&, per C+11 reference collapsing rules. For * example, int&& would become int&.) * * The final computed type will only *not* be an lvalue reference if T is void. * * mozilla::AddLvalueReference<int>::Type is int&; * mozilla::AddLvalueRference<volatile int&>::Type is volatile int&; * mozilla::AddLvalueReference<void*>::Type is void*&; * mozilla::AddLvalueReference<void>::Type is void; * mozilla::AddLvalueReference<struct S&&>::Type is struct S&. */ template<typename T> struct AddLvalueReference : detail::AddLvalueReferenceHelper<T> {}; namespace detail { template<typename T, Voidness V = IsVoid<T>::value ? TIsVoid : TIsNotVoid> struct AddRvalueReferenceHelper; template<typename T> struct AddRvalueReferenceHelper<T, TIsVoid> { typedef void Type; }; template<typename T> struct AddRvalueReferenceHelper<T, TIsNotVoid> { typedef T&& Type; }; } // namespace detail /** * AddRvalueReference adds an rvalue && reference to T if one isn't already * present. (Note: adding an rvalue reference to an lvalue & reference in * essence keeps the &, per C+11 reference collapsing rules. For example, * int& would remain int&.) * * The final computed type will only *not* be a reference if T is void. * * mozilla::AddRvalueReference<int>::Type is int&&; * mozilla::AddRvalueRference<volatile int&>::Type is volatile int&; * mozilla::AddRvalueRference<const int&&>::Type is const int&&; * mozilla::AddRvalueReference<void*>::Type is void*&&; * mozilla::AddRvalueReference<void>::Type is void; * mozilla::AddRvalueReference<struct S&>::Type is struct S&. */ template<typename T> struct AddRvalueReference : detail::AddRvalueReferenceHelper<T> {}; /* 20.9.7.3 Sign modifications [meta.trans.sign] */ template<bool B, typename T = void> struct EnableIf; namespace detail { template<bool MakeConst, typename T> struct WithC : Conditional<MakeConst, const T, T> {}; template<bool MakeVolatile, typename T> struct WithV : Conditional<MakeVolatile, volatile T, T> {}; template<bool MakeConst, bool MakeVolatile, typename T> struct WithCV : WithC<MakeConst, typename WithV<MakeVolatile, T>::Type> {}; template<typename T> struct CorrespondingSigned; template<> struct CorrespondingSigned<char> { typedef signed char Type; }; template<> struct CorrespondingSigned<unsigned char> { typedef signed char Type; }; template<> struct CorrespondingSigned<unsigned short> { typedef short Type; }; template<> struct CorrespondingSigned<unsigned int> { typedef int Type; }; template<> struct CorrespondingSigned<unsigned long> { typedef long Type; }; template<> struct CorrespondingSigned<unsigned long long> { typedef long long Type; }; template<typename T, typename CVRemoved = typename RemoveCV<T>::Type, bool IsSignedIntegerType = IsSigned<CVRemoved>::value && !IsSame<char, CVRemoved>::value> struct MakeSigned; template<typename T, typename CVRemoved> struct MakeSigned<T, CVRemoved, true> { typedef T Type; }; template<typename T, typename CVRemoved> struct MakeSigned<T, CVRemoved, false> : WithCV<IsConst<T>::value, IsVolatile<T>::value, typename CorrespondingSigned<CVRemoved>::Type> {}; } // namespace detail /** * MakeSigned produces the corresponding signed integer type for a given * integral type T, with the const/volatile qualifiers of T. T must be a * possibly-const/volatile-qualified integral type that isn't bool. * * If T is already a signed integer type (not including char!), then T is * produced. * * Otherwise, if T is an unsigned integer type, the signed variety of T, with * T's const/volatile qualifiers, is produced. * * Otherwise, the integral type of the same size as T, with the lowest rank, * with T's const/volatile qualifiers, is produced. (This basically only acts * to produce signed char when T = char.) * * mozilla::MakeSigned<unsigned long>::Type is signed long; * mozilla::MakeSigned<volatile int>::Type is volatile int; * mozilla::MakeSigned<const unsigned short>::Type is const signed short; * mozilla::MakeSigned<const char>::Type is const signed char; * mozilla::MakeSigned<bool> is an error; * mozilla::MakeSigned<void*> is an error. */ template<typename T> struct MakeSigned : EnableIf<IsIntegral<T>::value && !IsSame<bool, typename RemoveCV<T>::Type>::value, typename detail::MakeSigned<T> >::Type {}; namespace detail { template<typename T> struct CorrespondingUnsigned; template<> struct CorrespondingUnsigned<char> { typedef unsigned char Type; }; template<> struct CorrespondingUnsigned<signed char> { typedef unsigned char Type; }; template<> struct CorrespondingUnsigned<short> { typedef unsigned short Type; }; template<> struct CorrespondingUnsigned<int> { typedef unsigned int Type; }; template<> struct CorrespondingUnsigned<long> { typedef unsigned long Type; }; template<> struct CorrespondingUnsigned<long long> { typedef unsigned long long Type; }; template<typename T, typename CVRemoved = typename RemoveCV<T>::Type, bool IsUnsignedIntegerType = IsUnsigned<CVRemoved>::value && !IsSame<char, CVRemoved>::value> struct MakeUnsigned; template<typename T, typename CVRemoved> struct MakeUnsigned<T, CVRemoved, true> { typedef T Type; }; template<typename T, typename CVRemoved> struct MakeUnsigned<T, CVRemoved, false> : WithCV<IsConst<T>::value, IsVolatile<T>::value, typename CorrespondingUnsigned<CVRemoved>::Type> {}; } // namespace detail /** * MakeUnsigned produces the corresponding unsigned integer type for a given * integral type T, with the const/volatile qualifiers of T. T must be a * possibly-const/volatile-qualified integral type that isn't bool. * * If T is already an unsigned integer type (not including char!), then T is * produced. * * Otherwise, if T is an signed integer type, the unsigned variety of T, with * T's const/volatile qualifiers, is produced. * * Otherwise, the unsigned integral type of the same size as T, with the lowest * rank, with T's const/volatile qualifiers, is produced. (This basically only * acts to produce unsigned char when T = char.) * * mozilla::MakeUnsigned<signed long>::Type is unsigned long; * mozilla::MakeUnsigned<volatile unsigned int>::Type is volatile unsigned int; * mozilla::MakeUnsigned<const signed short>::Type is const unsigned short; * mozilla::MakeUnsigned<const char>::Type is const unsigned char; * mozilla::MakeUnsigned<bool> is an error; * mozilla::MakeUnsigned<void*> is an error. */ template<typename T> struct MakeUnsigned : EnableIf<IsIntegral<T>::value && !IsSame<bool, typename RemoveCV<T>::Type>::value, typename detail::MakeUnsigned<T> >::Type {}; /* 20.9.7.4 Array modifications [meta.trans.arr] */ /** * RemoveExtent produces either the type of the elements of the array T, or T * itself. * * mozilla::RemoveExtent<int>::Type is int; * mozilla::RemoveExtent<const int[]>::Type is const int; * mozilla::RemoveExtent<volatile int[5]>::Type is volatile int; * mozilla::RemoveExtent<long[][17]>::Type is long[17]. */ template<typename T> struct RemoveExtent { typedef T Type; }; template<typename T> struct RemoveExtent<T[]> { typedef T Type; }; template<typename T, decltype(sizeof(1)) N> struct RemoveExtent<T[N]> { typedef T Type; }; /* 20.9.7.5 Pointer modifications [meta.trans.ptr] */ namespace detail { template<typename T, typename CVRemoved> struct RemovePointerHelper { typedef T Type; }; template<typename T, typename Pointee> struct RemovePointerHelper<T, Pointee*> { typedef Pointee Type; }; } // namespace detail /** * Produces the pointed-to type if a pointer is provided, else returns the input * type. Note that this does not dereference pointer-to-member pointers. * * struct S { bool m; void f(); }; * mozilla::RemovePointer<int>::Type is int; * mozilla::RemovePointer<int*>::Type is int; * mozilla::RemovePointer<int* const>::Type is int; * mozilla::RemovePointer<int* volatile>::Type is int; * mozilla::RemovePointer<const long*>::Type is const long; * mozilla::RemovePointer<void* const>::Type is void; * mozilla::RemovePointer<void (S::*)()>::Type is void (S::*)(); * mozilla::RemovePointer<void (*)()>::Type is void(); * mozilla::RemovePointer<bool S::*>::Type is bool S::*. */ template<typename T> struct RemovePointer : detail::RemovePointerHelper<T, typename RemoveCV<T>::Type> {}; /** * Converts T& to T*. Otherwise returns T* given T. Note that C++17 wants * std::add_pointer to work differently for function types. We don't implement * that behavior here. * * mozilla::AddPointer<int> is int*; * mozilla::AddPointer<int*> is int**; * mozilla::AddPointer<int&> is int*; * mozilla::AddPointer<int* const> is int** const. */ template<typename T> struct AddPointer { typedef typename RemoveReference<T>::Type* Type; }; /* 20.9.7.6 Other transformations [meta.trans.other] */ /** * EnableIf is a struct containing a typedef of T if and only if B is true. * * mozilla::EnableIf<true, int>::Type is int; * mozilla::EnableIf<false, int>::Type is a compile-time error. * * Use this template to implement SFINAE-style (Substitution Failure Is not An * Error) requirements. For example, you might use it to impose a restriction * on a template parameter: * * template<typename T> * class PodVector // vector optimized to store POD (memcpy-able) types * { * EnableIf<IsPod<T>::value, T>::Type* vector; * size_t length; * ... * }; */ template<bool B, typename T> struct EnableIf {}; template<typename T> struct EnableIf<true, T> { typedef T Type; }; /** * Conditional selects a class between two, depending on a given boolean value. * * mozilla::Conditional<true, A, B>::Type is A; * mozilla::Conditional<false, A, B>::Type is B; */ template<bool Condition, typename A, typename B> struct Conditional { typedef A Type; }; template<class A, class B> struct Conditional<false, A, B> { typedef B Type; }; namespace detail { template<typename U, bool IsArray = IsArray<U>::value, bool IsFunction = IsFunction<U>::value> struct DecaySelector; template<typename U> struct DecaySelector<U, false, false> { typedef typename RemoveCV<U>::Type Type; }; template<typename U> struct DecaySelector<U, true, false> { typedef typename RemoveExtent<U>::Type* Type; }; template<typename U> struct DecaySelector<U, false, true> { typedef typename AddPointer<U>::Type Type; }; }; // namespace detail /** * Strips const/volatile off a type and decays it from an lvalue to an * rvalue. So function types are converted to function pointers, arrays to * pointers, and references are removed. * * mozilla::Decay<int>::Type is int * mozilla::Decay<int&>::Type is int * mozilla::Decay<int&&>::Type is int * mozilla::Decay<const int&>::Type is int * mozilla::Decay<int[2]>::Type is int* * mozilla::Decay<int(int)>::Type is int(*)(int) */ template<typename T> class Decay : public detail::DecaySelector<typename RemoveReference<T>::Type> { }; } /* namespace mozilla */ #endif /* mozilla_TypeTraits_h */