Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is the documentation for a snapshot of the develop branch, built from commit aa557371a1.
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Class template basic_any

boost::anys::basic_any — A class with customizable Small Object Optimization whose instances can hold instances of any type that satisfies ValueType requirements. Use boost::any instead if not sure.

Synopsis

// In header: <boost/any/basic_any.hpp>

template<std::size_t OptimizeForSize, std::size_t OptimizeForAlignment> 
class basic_any {
public:
  // construct/copy/destruct
  basic_any();
  basic_any(const basic_any &);
  basic_any(basic_any &&);
  template<typename ValueType> basic_any(const ValueType &);
  template<typename ValueType> basic_any(ValueType &&);
  basic_any & operator=(const basic_any &);
  basic_any & operator=(basic_any &&);
  template<typename ValueType> basic_any & operator=(const ValueType &);
  template<typename ValueType> basic_any & operator=(ValueType &&);
  ~basic_any();

  // modifiers
  basic_any & swap(basic_any &);

  // queries
  bool empty() const;
  const std::type_info & type() const;
};

Description

boost::anys::basic_any is the drop-in replacement for boost::any that provides controll over Small Object Optimization via OptimizeForSize and OptimizeForAlignment template parameters.

There are certain applications that require boost::any functionality, do know the typical/maximal size of the stored object and wish to avoid dynamic memory allocation overhead. For the convenience such applications may create a typedef for basic_any with the OptimizeForSize and OptimizeForAlignment template parameters set to typical/maximal size and alignment of types respectively. Memory allocation would be avoided for storing nothrow move constructible types with size and alignment less than or equal to the OptimizeForSize and OptimizeForAlignment values.

Otherwise just use boost::any.

basic_any public construct/copy/destruct

  1. basic_any();

    Postconditions:

    this->empty()
  2. basic_any(const basic_any & other);

    Effects:

    Copy constructor that copies content of other into new instance, so that any content is equivalent in both type and value to the content of other, or empty if other is empty.

    Throws:

    May fail with a std::bad_alloc exception or any exceptions arising from the copy constructor of the contained type.
  3. basic_any(basic_any && other);

    Effects:

    Move constructor that moves content of other into new instance and leaves other empty.

    Postconditions:

    other->empty()

    Throws:

    Nothing.
  4. template<typename ValueType> basic_any(const ValueType & value);

    Effects:

    Makes a copy of value, so that the initial content of the new instance is equivalent in both type and value to value.

    Does not dynamically allocate if ValueType is nothrow move constructible and sizeof(value) <= OptimizeForSize && alignof(value) <=OptimizeForAlignment.

    Throws:

    std::bad_alloc or any exceptions arising from the copy constructor of the contained type.
  5. template<typename ValueType> basic_any(ValueType && value);

    Effects:

    Forwards value, so that the initial content of the new instance is equivalent in both type and value to value before the forward.

    Does not dynamically allocate if ValueType is nothrow move constructible and sizeof(value) <= OptimizeForSize && alignof(value) <=OptimizeForAlignment.

    Throws:

    std::bad_alloc or any exceptions arising from the move or copy constructor of the contained type.
  6. basic_any & operator=(const basic_any & rhs);

    Effects:

    Copies content of rhs into current instance, discarding previous content, so that the new content is equivalent in both type and value to the content of rhs, or empty if rhs.empty().

    Throws:

    std::bad_alloc or any exceptions arising from the copy constructor of the contained type. Assignment satisfies the strong guarantee of exception safety.
  7. basic_any & operator=(basic_any && rhs);

    Effects:

    Moves content of rhs into current instance, discarding previous content, so that the new content is equivalent in both type and value to the content of rhs before move, or empty if rhs.empty().

    Postconditions:

    rhs->empty()

    Throws:

    Nothing.
  8. template<typename ValueType> basic_any & operator=(const ValueType & rhs);

    Effects:

    Makes a copy of rhs, discarding previous content, so that the new content of is equivalent in both type and value to rhs.

    Does not dynamically allocate if ValueType is nothrow move constructible and sizeof(value) <= OptimizeForSize && alignof(value) <=OptimizeForAlignment.

    Throws:

    std::bad_alloc or any exceptions arising from the copy constructor of the contained type. Assignment satisfies the strong guarantee of exception safety.
  9. template<typename ValueType> basic_any & operator=(ValueType && rhs);

    Effects:

    Forwards rhs, discarding previous content, so that the new content of is equivalent in both type and value to rhs before forward.

    Does not dynamically allocate if ValueType is nothrow move constructible and sizeof(value) <= OptimizeForSize && alignof(value) <=OptimizeForAlignment.

    Throws:

    std::bad_alloc or any exceptions arising from the move or copy constructor of the contained type. Assignment satisfies the strong guarantee of exception safety.
  10. ~basic_any();

    Effects:

    Releases any and all resources used in management of instance.

    Throws:

    Nothing.

basic_any modifiers

  1. basic_any & swap(basic_any & rhs);

    Effects:

    Exchange of the contents of *this and rhs.

    Returns:

    *this

    Throws:

    Nothing.

basic_any queries

  1. bool empty() const;

    Returns:

    true if instance is empty, otherwise false.

    Throws:

    Nothing.
  2. const std::type_info & type() const;

    Returns:

    the typeid of the contained value if instance is non-empty, otherwise typeid(void).

    Notes:

    Useful for querying against types known either at compile time or only at runtime.

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