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Simplify <type_traits> implementations.
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This patch rewrites a number of old meta-function implementations
that assumed const/volatile could not be safely applied to all types.
This is no longer the case, though for some types (Ex function types),
the const qualifier can be ignored.

The largest improvement in this patch is the reduction of is_function.
Thanks to Matt Calabrese for the improved implementation.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@367749 91177308-0d34-0410-b5e6-96231b3b80d8
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@EricWF
EricWF committed Aug 3, 2019
1 parent 3e9af5a commit 871b040
Showing 1 changed file with 36 additions and 67 deletions.
103 changes: 36 additions & 67 deletions include/type_traits
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Original file line number Diff line number Diff line change
Expand Up @@ -886,56 +886,40 @@ _LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_class_v

// is_function

namespace __libcpp_is_function_imp
{
struct __dummy_type {};
template <class _Tp> char __test(_Tp*);
template <class _Tp> char __test(__dummy_type);
template <class _Tp> __two __test(...);
template <class _Tp> _Tp& __source(int);
template <class _Tp> __dummy_type __source(...);
}

template <class _Tp, bool = is_class<_Tp>::value ||
is_union<_Tp>::value ||
is_void<_Tp>::value ||
is_reference<_Tp>::value ||
__is_nullptr_t<_Tp>::value >
struct __libcpp_is_function
: public integral_constant<bool, sizeof(__libcpp_is_function_imp::__test<_Tp>(__libcpp_is_function_imp::__source<_Tp>(0))) == 1>
{};
template <class _Tp> struct __libcpp_is_function<_Tp, true> : public false_type {};

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_function
: public __libcpp_is_function<_Tp> {};
: public _BoolConstant<
#ifdef __clang__
__is_function(_Tp)
#else
!(is_reference<_Tp>::value || is_const<const _Tp>::value)
#endif
> {};


#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
_LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_function_v
= is_function<_Tp>::value;
#endif

// is_member_function_pointer

// template <class _Tp> struct __libcpp_is_member_function_pointer : public false_type {};
// template <class _Tp, class _Up> struct __libcpp_is_member_function_pointer<_Tp _Up::*> : public is_function<_Tp> {};
//

template <class _MP, bool _IsMemberFunctionPtr, bool _IsMemberObjectPtr>
struct __member_pointer_traits_imp
{ // forward declaration; specializations later
template <class _Tp> struct __libcpp_is_member_pointer {
enum {
__is_member = false,
__is_func = false,
__is_obj = false
};
};
template <class _Tp, class _Up> struct __libcpp_is_member_pointer<_Tp _Up::*> {
enum {
__is_member = true,
__is_func = is_function<_Tp>::value,
__is_obj = !__is_func,
};
};


template <class _Tp> struct __libcpp_is_member_function_pointer
: public false_type {};

template <class _Ret, class _Class>
struct __libcpp_is_member_function_pointer<_Ret _Class::*>
: public is_function<_Ret> {};

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_member_function_pointer
: public __libcpp_is_member_function_pointer<typename remove_cv<_Tp>::type>::type {};
: public _BoolConstant< __libcpp_is_member_pointer<typename remove_cv<_Tp>::type>::__is_func > {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
Expand All @@ -945,11 +929,8 @@ _LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_member_function_pointer_v

// is_member_pointer

template <class _Tp> struct __libcpp_is_member_pointer : public false_type {};
template <class _Tp, class _Up> struct __libcpp_is_member_pointer<_Tp _Up::*> : public true_type {};

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_member_pointer
: public __libcpp_is_member_pointer<typename remove_cv<_Tp>::type> {};
: public _BoolConstant< __libcpp_is_member_pointer<typename remove_cv<_Tp>::type>::__is_member > {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
Expand All @@ -960,8 +941,7 @@ _LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_member_pointer_v
// is_member_object_pointer

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_member_object_pointer
: public integral_constant<bool, is_member_pointer<_Tp>::value &&
!is_member_function_pointer<_Tp>::value> {};
: public _BoolConstant< __libcpp_is_member_pointer<typename remove_cv<_Tp>::type>::__is_obj > {};

#if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
template <class _Tp>
Expand Down Expand Up @@ -1080,42 +1060,28 @@ struct __is_referenceable : integral_constant<bool,

// add_const

template <class _Tp, bool = is_reference<_Tp>::value ||
is_function<_Tp>::value ||
is_const<_Tp>::value >
struct __add_const {typedef _LIBCPP_NODEBUG_TYPE _Tp type;};

template <class _Tp>
struct __add_const<_Tp, false> {typedef _LIBCPP_NODEBUG_TYPE const _Tp type;};

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS add_const
{typedef _LIBCPP_NODEBUG_TYPE typename __add_const<_Tp>::type type;};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS add_const {
typedef _LIBCPP_NODEBUG_TYPE const _Tp type;
};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using add_const_t = typename add_const<_Tp>::type;
#endif

// add_volatile

template <class _Tp, bool = is_reference<_Tp>::value ||
is_function<_Tp>::value ||
is_volatile<_Tp>::value >
struct __add_volatile {typedef _Tp type;};

template <class _Tp>
struct __add_volatile<_Tp, false> {typedef volatile _Tp type;};

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS add_volatile
{typedef _LIBCPP_NODEBUG_TYPE typename __add_volatile<_Tp>::type type;};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS add_volatile {
typedef _LIBCPP_NODEBUG_TYPE volatile _Tp type;
};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using add_volatile_t = typename add_volatile<_Tp>::type;
#endif

// add_cv

template <class _Tp> struct _LIBCPP_TEMPLATE_VIS add_cv
{typedef _LIBCPP_NODEBUG_TYPE typename add_const<typename add_volatile<_Tp>::type>::type type;};
template <class _Tp> struct _LIBCPP_TEMPLATE_VIS add_cv {
typedef _LIBCPP_NODEBUG_TYPE const volatile _Tp type;
};

#if _LIBCPP_STD_VER > 11
template <class _Tp> using add_cv_t = typename add_cv<_Tp>::type;
Expand Down Expand Up @@ -2307,6 +2273,9 @@ __decay_copy(_Tp&& __t)
return _VSTD::forward<_Tp>(__t);
}

template <class _MP, bool _IsMemberFunctionPtr, bool _IsMemberObjectPtr>
struct __member_pointer_traits_imp;

template <class _Rp, class _Class, class ..._Param>
struct __member_pointer_traits_imp<_Rp (_Class::*)(_Param...), true, false>
{
Expand Down

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