Annex D (normative) Compatibility features [depr]

The class strstreambuf associates the input sequence, and possibly the output sequence, with an object of some character array type, whose elements store arbitrary values. The array object has several attributes.

[ Note: For the sake of exposition, these are represented as elements of a bitmask type (indicated here as T1) called strstate. The elements are:

• (2.1)

  allocated, set when a dynamic array object has been allocated, and hence should be freed by the destructor for the strstreambuf object;

• (2.2)

  constant, set when the array object has const elements, so the output sequence cannot be written;

• (2.3)

  dynamic, set when the array object is allocated (or reallocated) as necessary to hold a character sequence that can change in length;

• (2.4)

  frozen, set when the program has requested that the array object not be altered, reallocated, or freed.

 — end note ]

[ Note: For the sake of exposition, the maintained data is presented here as:

• (3.1)

  strstate strmode, the attributes of the array object associated with the strstreambuf object;

• (3.2)

  int alsize, the suggested minimum size for a dynamic array object;

• (3.3)

  void* (*palloc)(size_t), points to the function to call to allocate a dynamic array object;

• (3.4)

  void (*pfree)(void*), points to the function to call to free a dynamic array object.

 — end note ]

Each object of class strstreambuf has a seekable area, delimited by the pointers seeklow and seekhigh. If gnext is a null pointer, the seekable area is undefined. Otherwise, seeklow equals gbeg and seekhigh is either pend, if pend is not a null pointer, or gend.

The class istrstream supports the reading of objects of class strstreambuf. It supplies a strstreambuf object to control the associated array object. For the sake of exposition, the maintained data is presented here as:

• (1.1)

  sb, the strstreambuf object.

The class ostrstream supports the writing of objects of class strstreambuf. It supplies a strstreambuf object to control the associated array object. For the sake of exposition, the maintained data is presented here as:

• (1.1)

  sb, the strstreambuf object.

The class strstream supports reading and writing from objects of class strstreambuf. It supplies a strstreambuf object to control the associated array object. For the sake of exposition, the maintained data is presented here as:

• (1.1)

  sb, the strstreambuf object.

A call wrapper ([func.def]) may have a weak result type. If it does, the type of its member type result_type is based on the type T of the wrapper's target object:

• (1.1)

  if T is a pointer to function type, result_type shall be a synonym for the return type of T;

• (1.2)

  if T is a pointer to member function, result_type shall be a synonym for the return type of T;

• (1.3)

  if T is a class type and the qualified-id T::result_type is valid and denotes a type ([temp.deduct]), then result_type shall be a synonym for T::result_type;

• (1.4)

  otherwise result_type shall not be defined.

To enable old function adaptors to manipulate function objects that take one or two arguments, many of the function objects in this standard correspondingly provide typedef-names argument_type and result_type for function objects that take one argument and first_argument_type, second_argument_type, and result_type for function objects that take two arguments.

The following member names are defined in addition to names specified in Clause [function.objects]:

namespace std {
  template<class T> struct owner_less<shared_ptr<T>> {
    using result_type          = bool;
    using first_argument_type  = shared_ptr<T>;
    using second_argument_type = shared_ptr<T>;
  };

  template<class T> struct owner_less<weak_ptr<T>> {
    using result_type          = bool;
    using first_argument_type  = weak_ptr<T>;
    using second_argument_type = weak_ptr<T>;
  };

  template <class T> class reference_wrapper {
  public :
    using result_type          = see below; // not always defined
    using argument_type        = see below; // not always defined
    using first_argument_type  = see below; // not always defined
    using second_argument_type = see below; // not always defined
  };

  template <class T> struct plus {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = T;
  };

  template <class T> struct minus {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = T;
  };

  template <class T> struct multiplies {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = T;
  };

  template <class T> struct divides {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = T;
  };

  template <class T> struct modulus {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = T;
  };

  template <class T> struct negate {
    using argument_type = T;
    using result_type   = T;
  };

  template <class T> struct equal_to {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = bool;
  };

  template <class T> struct not_equal_to {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = bool;
  };

  template <class T> struct greater {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = bool;
  };

  template <class T> struct less {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = bool;
  };

  template <class T> struct greater_equal {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = bool;
  };

  template <class T> struct less_equal {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = bool;
  };

  template <class T> struct logical_and {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = bool;
  };

  template <class T> struct logical_or {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = bool;
  };

  template <class T> struct logical_not {
    using argument_type = T;
    using result_type   = bool;
  };

  template <class T> struct bit_and {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = T;
  };

  template <class T> struct bit_or {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = T;
  };

  template <class T> struct bit_xor {
    using first_argument_type  = T;
    using second_argument_type = T;
    using result_type          = T;
  };

  template <class T> struct bit_not {
    using argument_type = T;
    using result_type   = T;
  };

  template<class R, class T1>
  class function<R(T1)> {
  public:
    using argument_type = T1;
  };

  template<class R, class T1, class T2>
  class function<R(T1, T2)> {
  public:
    using first_argument_type  = T1;
    using second_argument_type = T2;
  };
}

reference_wrapper<T> has a weak result type ([depr.weak.result_type]). If T is a function type, result_type shall be a synonym for the return type of T.

The template specialization reference_wrapper<T> shall define a nested type named argument_type as a synonym for T1 only if the type T is any of the following:

• (4.1)

  a function type or a pointer to function type taking one argument of type T1

• (4.2)

  a pointer to member function R T0::f cv (where cv represents the member function's cv-qualifiers); the type T1 is cv T0*

• (4.3)

  a class type where the qualified-id T::argument_type is valid and denotes a type ([temp.deduct]); the type T1 is T::argument_type.

The template instantiation reference_wrapper<T> shall define two nested types named first_argument_type and second_argument_type as synonyms for T1 and T2, respectively, only if the type T is any of the following:

• (5.1)

  a function type or a pointer to function type taking two arguments of types T1 and T2

• (5.2)

  a pointer to member function R T0::f(T2) cv (where cv represents the member function's cv-qualifiers); the type T1 is cv T0*

• (5.3)

  a class type where the qualified-ids T::first_argument_type and T::second_argument_type are both valid and both denote types ([temp.deduct]); the type T1 is T::first_argument_type and the type T2 is T::second_argument_type.

All enabled specializations hash<Key> of hash ([unord.hash]) provide two nested types, result_type and argument_type, which shall be synonyms for size_t and Key, respectively.

The forwarding call wrapper g returned by a call to bind(f, bound_args...) ([func.bind.bind]) shall have a weak result type ([depr.weak.result_type]).

The forwarding call wrapper g returned by a call to bind<R>(f, bound_args...) ([func.bind.bind]) shall have a nested type result_type defined as a synonym for R.

The simple call wrapper returned from a call to mem_fn(pm) shall have a nested type result_type that is a synonym for the return type of pm when pm is a pointer to member function.

The simple call wrapper returned from a call to mem_fn(pm) shall define two nested types named argument_type and result_type as synonyms for cv T* and Ret, respectively, when pm is a pointer to member function with cv-qualifier cv and taking no arguments, where Ret is pm's return type.

The simple call wrapper returned from a call to mem_fn(pm) shall define three nested types named first_argument_type, second_argument_type, and result_type as synonyms for cv T*, T1, and Ret, respectively, when pm is a pointer to member function with cv-qualifier cv and taking one argument of type T1, where Ret is pm's return type.

The following member names are defined in addition to names specified in Clause [containers]:

namespace std {
  template <class Key, class T, class Compare, class Allocator>
  class map<Key, T, Compare, Allocator>::value_compare {
  public:
    using result_type          = bool;
    using first_argument_type  = value_type;
    using second_argument_type = value_type;
  };

  template <class Key, class T, class Compare, class Allocator>
  class multimap<Key, T, Compare, Allocator>::value_compare {
  public:
    using result_type          = bool;
    using first_argument_type  = value_type;
    using second_argument_type = value_type;
  };
}

The header <functional> has the following additions:

namespace std {
  template <class Predicate> class unary_negate;
  template <class Predicate>
    constexpr unary_negate<Predicate> not1(const Predicate&);
  template <class Predicate> class binary_negate;
  template <class Predicate>
    constexpr binary_negate<Predicate> not2(const Predicate&);
}

Negators not1 and not2 take a unary and a binary predicate, respectively, and return their logical negations ([expr.unary.op]).

template <class Predicate>
class unary_negate {
public:
  constexpr explicit unary_negate(const Predicate& pred);
  constexpr bool operator()(const typename Predicate::argument_type& x) const;
  using argument_type = typename Predicate::argument_type;
  using result_type   = bool;
};

constexpr bool operator()(const typename Predicate::argument_type& x) const;

The header <iterator> has the following addition:

namespace std {
  template<class Category, class T, class Distance = ptrdiff_t,
    class Pointer = T*, class Reference = T&>
  struct iterator {
    using iterator_category = Category;
    using value_type        = T;
    using difference_type   = Distance;
    using pointer           = Pointer;
    using reference         = Reference;
  };
}

The iterator template may be used as a base class to ease the definition of required types for new iterators.

[ Note: If the new iterator type is a class template, then these aliases will not be visible from within the iterator class's template definition, but only to callers of that class. — end note ]

[ Example: If a C++ program wants to define a bidirectional iterator for some data structure containing double and such that it works on a large memory model of the implementation, it can do so with:

class MyIterator :
  public iterator<bidirectional_iterator_tag, double, long, T*, T&> {
  // code implementing ++, etc.
};

 — end example ]