ceph/src/boost/libs/python/doc/reference/type_id.qbk

   1 [section boost/python/type_id.hpp]
   2 [section Introduction]
   3 <boost/python/type_id.hpp> provides types and functions for runtime type identification like those of of `<typeinfo>`. It exists mostly to work around certain compiler bugs and platform-dependent interactions with shared libraries.
   4 [endsect]
   5 [section Class template `type_info`]
   6 `type_info` instances identify a type. As `std::type_info` is specified to (but unlike its implementation in some compilers), `boost::python::type_info` never represents top-level references or cv-qualification (see section 5.2.8 in the C++ standard). Unlike `std::type_info`, `boost::python::type_info` instances are copyable, and comparisons always work reliably across shared library boundaries.
   7 ``
   8 namespace boost { namespace python
   9 {
  10   class type_info : totally_ordered<type_info>
  11   {
  12   public:
  13     // constructor
  14     type_info(std::type_info const& = typeid(void));
  15
  16     // comparisons
  17     bool operator<(type_info const& rhs) const;
  18     bool operator==(type_info const& rhs) const;
  19
  20     // observers
  21     char const* name() const;
  22   };
  23 }}
  24 ``
  25 [section Class template `type_info` constructor]
  26 ``type_info(std::type_info const& = typeid(void));``
  27 [variablelist
  28 [[Effects][constructs a `type_info` object which identifies the same type as its argument.]]
  29 [[Rationale][Since it is occasionally necessary to make an array of `type_info` objects a benign default argument is supplied. Note: this constructor does not correct for non-conformance of compiler `typeid()` implementations. See `type_id`, below.]]
  30 ]
  31 [endsect]
  32 [section Class template `type_info` comparison]
  33 ``bool operator<(type_info const &rhs) const;``
  34 [variablelist
  35 [[Effects][yields a total order over `type_info` objects.]]
  36 ]
  37 ``bool operator==(type_info const &rhs) const;``
  38 [variablelist
  39 [[Returns][`true` iff the two values describe the same type.]]
  40 [[Note][The use of `totally_ordered<type_info>` as a private base class supplies operators `<=`, `>=`, `>`, and `!=`]]
  41 ]
  42 [endsect]
  43 [section Class template `type_info` observers]
  44 ``
  45 char const* name() const;
  46 ``
  47 [variablelist
  48 [[Returns][The result of calling `name()` on the argument used to construct the object.]]
  49 ]
  50 [endsect]
  51 [endsect]
  52 [section Functions]
  53 ``
  54 std::ostream& operator<<(std::ostream&s, type_info const&x);
  55 ``
  56 [variablelist
  57 [[Effects][Writes a description of the type described by to `x` into s.]]
  58 [[Rationale][Not every C++ implementation provides a truly human-readable `type_info::name()` string, but for some we may be able to decode the string and produce a reasonable representation.]]
  59 [[Note][On some non-conforming C++ implementations, the code is not actually as simple as described above; the semantics are adjusted to work as-if the C++ implementation were conforming.]]
  60 ]
  61 ``
  62 template <class T> type_info type_id()
  63 ``
  64 [variablelist
  65 [[Returns][`type_info(typeid(T))`]]
  66 [[Note][On some non-conforming C++ implementations, the code is not actually as simple as described above; the semantics are adjusted to work as-if the C++ implementation were conforming.]]
  67 ]
  68 [endsect]
  69 [section Example]
  70 The following example, though silly, illustrates how the type_id facility might be used
  71 ``
  72 #include <boost/python/type_id.hpp>
  73
  74 // Returns true iff the user passes an int argument
  75 template <class T>
  76 bool is_int(T x)
  77 {
  78    using boost::python::type_id;
  79    return type_id<T>() == type_id<int>();
  80 }
  81 ``
  82 [endsect]
  83 [endsect]