type_traits.qbk

C++的一个好库。。。现在很流行

   };
  
__type The same type as `T const` for all `T`.  

__std_ref 3.9.3.

__compat If the compiler does not support partial specialization of class-templates
then this template will compile, but the member `type` will always be the same as 
type `T` except where __transform_workaround have been applied.

__header ` #include <boost/type_traits/add_const.hpp>` or ` #include <boost/type_traits.hpp>`

[table Examples

[ [Expression] [Result Type]]

[[`add_const<int>::type`][`int const`]]

[[`add_const<int&>::type`] [`int&`]]

[[`add_const<int*>::type`] [`int* const`]]

[[`add_const<int const>::type`] [`int const`]]

]

[endsect]

[section:add_cv add_cv]

   template <class T>
   struct add_cv
   {
      typedef __below type;
   };
  
__type The same type as `T const volatile` for all `T`.  

__std_ref 3.9.3.

__compat If the compiler does not support partial specialization of class-templates
then this template will compile, but the member `type` will always be the same as 
type `T` except where __transform_workaround have been applied.

__header ` #include <boost/type_traits/add_cv.hpp>` or ` #include <boost/type_traits.hpp>`

[table Examples

[ [Expression] [Result Type]]

[[`add_cv<int>::type`][`int const volatile`]]

[[`add_cv<int&>::type`] [`int&`]]

[[`add_cv<int*>::type`] [`int* const volatile`]]

[[`add_cv<int const>::type`] [`int const volatile`]]

]

[endsect]

[section:add_pointer add_pointer]

   template <class T>
   struct add_pointer
   {
      typedef __below type;
   };
  
__type The same type as `remove_reference<T>::type*`.  

The rationale for this template
is that it produces the same type as `TYPEOF(&t)`, 
where `t` is an object of type `T`.

__std_ref 8.3.1.

__compat If the compiler does not support partial specialization of class-templates
then this template will compile, but the member `type` will always be the same as 
type `T` except where __transform_workaround have been applied.

__header ` #include <boost/type_traits/add_pointer.hpp>` or ` #include <boost/type_traits.hpp>`

[table Examples

[ [Expression] [Result Type]]

[[`add_pointer<int>::type`][`int*`]]

[[`add_pointer<int const&>::type`] [`int const*`]]

[[`add_pointer<int*>::type`] [`int**`]]

[[`add_pointer<int*&>::type`] [`int**`]]

]

[endsect]

[section:add_reference add_reference]

   template <class T>
   struct add_reference
   {
      typedef __below type;
   };
  
__type If `T` is not a reference type then `T&`, otherwise `T`.

__std_ref 8.3.2.

__compat If the compiler does not support partial specialization of class-templates
then this template will compile, but the member `type` will always be the same as 
type `T` except where __transform_workaround have been applied.

__header ` #include <boost/type_traits/add_reference.hpp>` or ` #include <boost/type_traits.hpp>`

[table Examples

[ [Expression] [Result Type]]

[[`add_reference<int>::type`][`int&`]]

[[`add_reference<int const&>::type`] [`int const&`]]

[[`add_reference<int*>::type`] [`int*&`]]

[[`add_reference<int*&>::type`] [`int*&`]]

]

[endsect]

[section:add_volatile add_volatile]

   template <class T>
   struct add_volatile
   {
      typedef __below type;
   };
  
__type The same type as `T volatile` for all `T`.  

__std_ref 3.9.3.

__compat If the compiler does not support partial specialization of class-templates
then this template will compile, but the member `type` will always be the same as 
type `T` except where __transform_workaround have been applied.

__header ` #include <boost/type_traits/add_volatile.hpp>` or ` #include <boost/type_traits.hpp>`

[table Examples

[ [Expression] [Result Type]]

[[`add_volatile<int>::type`][`int volatile`]]

[[`add_volatile<int&>::type`] [`int&`]]

[[`add_volatile<int*>::type`] [`int* volatile`]]

[[`add_volatile<int const>::type`] [`int const volatile`]]

]

[endsect]

[section:aligned_storage aligned_storage]

   template <std::size_t Size, std::size_t Align>
   struct aligned_storage
   {
      typedef __below type;
   };
  
__type a built-in or POD type with size `Size` and an alignment 
that is a multiple of `Align`.  

__header ` #include <boost/type_traits/aligned_storage.hpp>` or ` #include <boost/type_traits.hpp>`

[endsect]

[section:alignment_of alignment_of]
   template <class T>
   struct alignment_of : public __integral_constant<std::size_t, ALIGNOF(T)> {};
  
__inherit Class template alignment_of inherits from 
`__integral_constant<std::size_t, ALIGNOF(T)>`, where `ALIGNOF(T)` is the
alignment of type T.  

['Note: strictly speaking you should only rely on 
the value of `ALIGNOF(T)` being a multiple of the true alignment of T, although
in practice it does compute the correct value in all the cases we know about.]

__header ` #include <boost/type_traits/alignment_of.hpp>` or ` #include <boost/type_traits.hpp>`

__examples

[:`alignment_of<int>` inherits from `__integral_constant<std::size_t, ALIGNOF(int)>`.]

[:`alignment_of<char>::type` is the type `__integral_constant<std::size_t, ALIGNOF(char)>`.]

[:`alignment_of<double>::value` is an integral constant 
expression with value `ALIGNOF(double)`.]

[:`alignment_of<T>::value_type` is the type `std::size_t`.]

[endsect]

[section:extent extent]
   template <class T, std::size_t N = 0>
   struct extent : public __integral_constant<std::size_t, EXTENT(T,N)> {};
  
__inherit Class template extent inherits from `__integral_constant<std::size_t, EXTENT(T,N)>`, 
where `EXTENT(T,N)` is the number of elements in the N'th array dimention of type `T`.

If `T` is not an array type, or if `N > __rank<T>::value`, or if the N'th array bound
is incomplete, then `EXTENT(T,N)` is zero.

__header ` #include <boost/type_traits/extent.hpp>` or ` #include <boost/type_traits.hpp>`

__examples

[:`extent<int[1]>` inherits from `__integral_constant<std::size_t, 0>`.]

[:`extent<double[2][3][4], 1>::type` is the type `__integral_constant<std::size_t, 3>`.]

[:`extent<int[4]>::value` is an integral constant 
expression that evaluates to /4/.]

[:`extent<int[][2]>::value` is an integral constant 
expression that evaluates to /0/.]

[:`extent<int[][2], 1>::value` is an integral constant 
expression that evaluates to /2/.]

[:`extent<int*>::value` is an integral constant 
expression that evaluates to /0/.]

[:`extent<T>::value_type` is the type `std::size_t`.]

[endsect]

[section:function_traits function_traits]
[def __argN '''arg<replaceable>N</replaceable>_type''']

   template <class T>
   struct function_traits
   {
      static const std::size_t    arity = __below;
      typedef __below           result_type;
      typedef __below           __argN; 
   };

The class template function_traits will only compile if:

* The compiler supports partial specialization of class templates.
* The template argument `T` is a /function type/, note that this ['[*is not]] 
the same thing as a /pointer to a function/.

[table Function Traits Members 
[[Member] [Description]] 
[[`function_traits<T>::arity`] 
   [An integral constant expression that gives the number of arguments accepted by the function type `F`.]]
[[`function_traits<T>::result_type`] 
   [The type returned by function type `F`.]]
[[`function_traits<T>::__argN`] 
   [The '''<replaceable>N</replaceable>th''' argument type of function type `F`, where `1 <= N <= arity` of `F`.]]
]

[table Examples
[[Expression] [Result]] 
[[`function_traits<void (void)>::arity`] [An integral constant expression that has the value 0.]]
[[`function_traits<long (int)>::arity`] [An integral constant expression that has the value 1.]]
[[`function_traits<long (int, long, double, void*)>::arity`] [An integral constant expression that has the value 4.]]
[[`function_traits<void (void)>::result_type`] [The type `void`.]]
[[`function_traits<long (int)>::result_type`] [The type `long`.]]
[[`function_traits<long (int)>::arg0_type`] [The type `int`.]]
[[`function_traits<long (int, long, double, void*)>::arg3_type`] [The type `void*`.]]
[[`function_traits<long (int, long, double, void*)>::arg4_type`] [A compiler error: there is no `arg4_type` since there are only three arguments.]]
[[`function_traits<long (*)(void)>::arity`] [A compiler error: argument type is a /function pointer/, and not a /function type/.]]

]
   
[endsect]

[section:has_nothrow_assign has_nothrow_assign]

   template <class T>
   struct has_nothrow_assign : public __tof {};
  
__inherit If T is a (possibly cv-qualified) type with a non-throwing assignment-operator
then inherits from __true_type, otherwise inherits from __false_type.  Type `T`
must be a complete type.

__compat If the compiler does not support partial-specialization of class 
templates, then this template can not be used with function types.

Without some (as yet unspecified) help from the compiler, 
`has_nothrow_assign` will never report that a class or struct has a 
non-throwing assignment-operator; this is always safe, if possibly sub-optimal.
Currently (May 2005) only Visual C++ 8 has the necessary compiler support to ensure that this
trait "just works".

__header ` #include <boost/type_traits/has_nothrow_assign.hpp>` or ` #include <boost/type_traits.hpp>`

[endsect]

[section:has_nothrow_constructor has_nothrow_constructor]
   template <class T>
   struct has_nothrow_constructor : public __tof {};
  
__inherit If T is a (possibly cv-qualified) type with a non-throwing default-constructor
then inherits from __true_type, otherwise inherits from __false_type.  Type `T`
must be a complete type.

__compat If the compiler does not support partial-specialization of class 
templates, then this template can not be used with function types.

Without some (as yet unspecified) help from the compiler, 
`has_nothrow_constructor` will never report that a class or struct has a 
non-throwing default-constructor; this is always safe, if possibly sub-optimal.
Currently (May 2005) only Visual C++ 8 has the necessary compiler __intrinsics to ensure that this
trait "just works".

__header ` #include <boost/type_traits/has_nothrow_constructor.hpp>` or ` #include <boost/type_traits.hpp>`

[endsect]

[section:has_nothrow_copy has_nothrow_copy]
   template <class T>
   struct has_nothrow_copy : public __tof {};
  
__inherit If T is a (possibly cv-qualified) type with a non-throwing copy-constructor
then inherits from __true_type, otherwise inherits from __false_type.  Type `T`
must be a complete type.

__compat If the compiler does not support partial-specialization of class 
templates, then this template can not be used with function types.

Without some (as yet unspecified) help from the compiler, 
`has_nothrow_copy` will never report that a class or struct has a