The Tor Browser: mfbt/TypeTraits.h@97036ab72558 (annotated)

mfbt/TypeTraits.h@97036ab72558 (annotated)

mfbt/TypeTraits.h

Tue, 06 Jan 2015 21:39:09 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Tue, 06 Jan 2015 21:39:09 +0100
branch: TOR_BUG_9701
changeset 8: 97036ab72558
permissions: -rw-r--r--

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 /* -*- 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;
 /* 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 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 {};
 #ifdef MOZ_CHAR16_IS_NOT_WCHAR
 template<> struct IsIntegralHelper<char16_t>           : TrueType {};
 #endif
 } /* 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;
  *
  * Note that the behavior of IsIntegral on char16_t and char32_t is
  * unspecified.
  */
 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>
 {};
 /**
  * IsPointer determines whether a type is a pointer type (but not a pointer-to-
  * member type).
  *
  * mozilla::IsPointer<struct S*>::value is true;
  * mozilla::IsPointer<int**>::value is true;
  * mozilla::IsPointer<void (*)(void)>::value is true;
  * mozilla::IsPointer<int>::value is false;
  * mozilla::IsPointer<struct S>::value is false.
  */
 template<typename T>
 struct IsPointer : FalseType {};
 template<typename T>
 struct IsPointer<T*> : TrueType {};
 /**
  * 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>
 {};
 /* 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 {};
 #ifdef MOZ_CHAR16_IS_NOT_WCHAR
 template<> struct IsPod<char16_t>           : TrueType {};
 #endif
 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>
 struct IsSignedHelper;
 template<typename T>
 struct IsSignedHelper<T, true> : TrueType {};
 template<typename T>
 struct IsSignedHelper<T, false>
   : IntegralConstant<bool, IsArithmetic<T>::value && T(-1) < T(1)>
 {};
 } // 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|.
  *
  * Don't use this if the type might be user-defined!  You might or might not get
  * a compile error, depending.
  *
  * 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>
 struct IsUnsignedHelper;
 template<typename T>
 struct IsUnsignedHelper<T, true> : FalseType {};
 template<typename T>
 struct IsUnsignedHelper<T, false>
   : IntegralConstant<bool,
                      IsArithmetic<T>::value &&
                      (IsSame<typename RemoveCV<T>::Type, bool>::value ||
                       T(1) < T(-1))>
 {};
 } // namespace detail
 /**
  * IsUnsigned determines whether a type is an unsigned arithmetic type.
  *
  * Don't use this if the type might be user-defined!  You might or might not get
  * a compile error, depending.
  *
  * 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> {};
 /* 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:
     static From create();
     template<typename From1, typename To1>
     static char test(To to);
     template<typename From1, typename To1>
     static int test(...);
   public:
     static const bool value =
       sizeof(test<From, To>(create())) == 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!
  */
 template<typename From, typename To>
 struct IsConvertible
   : IntegralConstant<bool, detail::ConvertibleTester<From, To>::value>
 {};
 /* 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;
 };
 /* 20.9.7.3 Sign modifications [meta.trans.sign] */
 template<bool B, typename T = void>
 struct EnableIf;
 template<bool Condition, typename A, typename B>
 struct Conditional;
 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] */
 /* 20.9.7.5 Pointer modifications [meta.trans.ptr] */
 /* 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 mozilla */
 #endif /* mozilla_TypeTraits_h */

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mfbt/TypeTraits.h