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### unordered_set_of Reference

#### Header "boost/bimap/unordered_set_of.hpp" synopsis

    namespace boost {
    namespace bimaps {

    template
    <
        class KeyType,
        class HashFunctor   = hash< KeyType >,
        class EqualKey      = std::equal_to< KeyType >
    >
    struct unordered_set_of;

    template
    <
        class HashFunctor   = hash< _relation >,
        class EqualKey      = std::equal_to< _relation >
    >
    struct unordered_set_of_relation;

    } // namespace bimap
    } // namespace boost

#### Header "boost/bimap/unordered_multiset_of.hpp" synopsis

    namespace boost {
    namespace bimaps {

    template
    <
        class KeyType,
        class HashFunctor   = hash< KeyType >,
        class EqualKey      = std::equal_to< KeyType >
    >
    struct unordered_multiset_of;

    template
    <
        class HashFunctor   = hash< _relation >,
        class EqualKey      = std::equal_to< _relation >
    >
    struct unordered_multiset_of_relation;

    } // namespace bimap
    } // namespace boost

#### Collection type specifiers unordered_set_of and unordered_multiset_of

These collection types specifiers allow for set views without and with allowance of duplicate elements, respectively. The syntax of `set_of` and `multiset_of` coincide, thus we describe them in a grouped manner.

#### unordered_[multi]set_of Views

An unordered_[multi]set_of set view is a tr1::unordered[multi]set signature compatible interface to the underlying heap of elements contained in a `bimap`.

The interface and semantics of `unordered_[multi]set_of` views are modeled according to the proposal for unordered associative containers given in the C++ Standard Library Technical Report, also known as TR1. An `unordered_[multi]set_of` view is particularized according to a given `Hash` function object which returns hash values for the keys and a binary predicate `Pred` acting as an equivalence relation on values of Key.

There are two variants: unordered_set_of, which do not allow duplicate elements (with respect to its associated comparison predicate) and unordered_multiset_of, which accept those duplicates. The interface of these two variants is the same to a great extent, so they are documented together with their differences explicitly noted when they exist.

If you look the bimap by a side, you will use a map view and if you looked it as a whole you will be using a set view.

Except where noted, `unordered_[multi]set_of` views (both unique and non-unique) are models of `Unordered Associative Container`. Validity of iterators and references to elements is preserved in all cases. Occasionally, the exception safety guarantees provided are actually stronger than required by the extension draft. We only provide descriptions of those types and operations that are either not present in the concepts modeled or do not exactly conform to the requirements for unordered associative containers.

    namespace boost {
    namespace bimap {
    namespace views {

    template< -implementation defined parameter list- >
    class -implementation defined view name-
    {
        public:

        // types

        typedef -unspecified- key_type;
        typedef -unspecified- value_type;
        typedef -unspecified- key_compare;
        typedef -unspecified- value_compare;
        typedef -unspecified- hasher;
        typedef -unspecified- key_equal;
        typedef -unspecified- allocator_type;
        typedef -unspecified- reference;
        typedef -unspecified- const_reference;
        typedef -unspecified- iterator;
        typedef -unspecified- const_iterator;
        typedef -unspecified- size_type;
        typedef -unspecified- difference_type;
        typedef -unspecified- pointer;
        typedef -unspecified- const_pointer;
        typedef -unspecified- local_iterator;
        typedef -unspecified- const_local_iterator;

        typedef -unspecified- info_type;

        // construct/destroy/copy:

        this_type & operator=(const this_type & x);

        allocator_type get_allocator() const;

        // size and capacity

        bool      empty() const;
        size_type size() const;
        size_type max_size() const;

        // iterators

        iterator       begin();
        const_iterator begin() const;
        iterator       end();
        const_iterator end() const;

        // modifiers

        std::pair< iterator, bool > insert(const value_type & x);

        iterator insert(iterator position, const value_type & x);

        template< class InputIterator >
        void insert(InputIterator first, InputIterator last);

        iterator erase(iterator position);

        template< class CompatibleKey >
        size_type erase(const CompatibleKey & x);

        iterator erase(iterator first, iterator last);

        bool replace(iterator position, const value_type & x);

        // Only in map views
        // {

          template< class CompatibleKey >
          bool replace_key(iterator position, const CompatibleKey & x);

          template< class CompatibleData >
          bool replace_data(iterator position, const CompatibleData & x);

          template< class KeyModifier >
          bool modify_key(iterator position, KeyModifier mod);

          template< class DataModifier >
          bool modify_data(iterator position, DataModifier mod);

        // }

        void clear();

        // observers

        key_from_value key_extractor() const;
        hasher         hash_function() const;
        key_equal      key_eq() const;

        // lookup

        template< class CompatibleKey >
        iterator find(const CompatibleKey & x);

        template< class CompatibleKey >
        const_iterator find(const CompatibleKey & x) const;

        template< class CompatibleKey >
        size_type count(const CompatibleKey & x) const;

        template< class CompatibleKey >
        std::pair<iterator,iterator>
            equal_range(const CompatibleKey & x);

        template< class CompatibleKey >
        std::pair<const_iterator,const_iterator>
            equal_range(const CompatibleKey & x) const;

        // bucket interface

        size_type bucket_count() const;
        size_type max_bucket_count() const;
        size_type bucket_size(size_type n) const;
        size_type bucket(const key_type & k) const;

        local_iterator       begin(size_type n);
        const_local_iterator begin(size_type n) const;
        local_iterator       end(size_type n);
        const_local_iterator end(size_type n) const;

        // hash policy

        float load_factor() const;
        float max_load_factor() const;
        void  max_load_factor(float z);
        void  rehash(size_type n);

        // Only in maps views
        // {

        typedef -unspecified- data_type;

          // Only in for `unordered_set_of` collection type
          // {

          template<class CompatibleKey>
          const data_type & at(const CompatibleKey & k) const;

            // Only if the other collection type is mutable
            // {

            template<class CompatibleKey>
            data_type & operator[](const CompatibleKey & k);

            template<class CompatibleKey>
            data_type & at(const CompatibleKey & k);

            // }

            // Only if info_hook is used
            // {

            template< class CompatibleKey >
            info_type & info_at(const CompatibleKey & k);

            template< class CompatibleKey >
            const info_type & info_at(const CompatibleKey & k) const;

          // }

        // }

    };

    } // namespace views
    } // namespace bimap
    } // namespace boost

In the case of a `bimap< unordered_{multi}set_of<Left>, ... >`

In the set view:

    typedef signature-compatible with relation<       Left, ... > key_type;
    typedef signature-compatible with relation< const Left, ... > value_type;

In the left map view:

    typedef  Left  key_type;
    typedef  ...   data_type;

    typedef signature-compatible with std::pair< const Left, ... > value_type;

In the right map view:

    typedef  ...  key_type;
    typedef  Left data_type;

    typedef signature-compatible with std::pair< ... ,const Left > value_type;

##### Complexity signature

Here and in the descriptions of operations of `unordered_[multi]set_of` views, we adopt the scheme outlined in the complexity signature section. The complexity signature of `unordered_[multi]set_of` view is:

- copying: `c(n) = n * log(n)`,
- insertion: average case `i(n) = 1` (constant), worst case `i(n) = n`,
- hinted insertion: average case `h(n) = 1` (constant), worst case `h(n) = n`,
- deletion: average case `d(n) = 1` (constant), worst case `d(n) = n`,
- replacement:
  - if the new element key is equivalent to the original, `r(n) = 1` (constant),
  - otherwise, average case `r(n) = 1` (constant), worst case `r(n) = n`,
- modifying: average case `m(n) = 1` (constant), worst case `m(n) = n`.

##### Instantiation types

`unordered_[multi]set_of` views are instantiated internally to `bimap` specified by means of the collection type specifiers and the `bimap` itself. Instantiations are dependent on the following types:

- `Value` from `bimap`,
- `Allocator` from `bimap`,
- `Hash` from the collection type specifier,
- `Pred` from the collection type specifier.

`Hash` is a Unary Function taking a single argument of type `key_type` and returning a value of type `std::size_t` in the range `[0, std::numeric_limits<std::size_t>::max())`. Pred is a Binary Predicate inducing an equivalence relation on elements of `key_type`. It is required that the `Hash` object return the same value for keys equivalent under `Pred`.

##### Nested types

    iterator
    const_iterator
    local_iterator
    const_local_iterator

> These types are models of Forward Iterator.

##### Constructors, copy and assignment

As explained in the concepts section, views do not have public constructors or destructors. Assignment, on the other hand, is provided. Upon construction, `max_load_factor()` is 1.0.

    this_type & operator=(const this_type & x);

- Effects: `a = b`; where a and b are the `bimap` objects to which `*this` and x belong, respectively.
- Returns: `*this.`

##### Modifiers

    std::pair<iterator,bool> insert(const value_type & x);

- Effects: Inserts `x` into the `bimap` to which the view belongs if
  - the view is non-unique OR no other element with equivalent key exists,
  - AND insertion is allowed by all other views of the `bimap`.
- Returns: The return value is a pair `p`. `p.second` is `true` if and only if insertion took place. On successful insertion, `p.first` points to the element inserted; otherwise, `p.first` points to an element that caused the insertion to be banned. Note that more than one element can be causing insertion not to be allowed.
- Complexity: O(I(n)).
- Exception safety: Strong.

    iterator insert(iterator position, const value_type & x);

- Requires: `position` is a valid iterator of the view.
- Effects: `position` is used as a hint to improve the efficiency of the operation. Inserts `x` into the `bimap` to which the view belongs if
  - the view is non-unique OR no other element with equivalent key exists,
  - AND insertion is allowed by all other views of the `bimap`.
- Returns: On successful insertion, an iterator to the newly inserted element. Otherwise, an iterator to an element that caused the insertion to be banned. Note that more than one element can be causing insertion not to be allowed.
- Complexity: O(H(n)).
- Exception safety: Strong.

    template< class InputIterator>
    void insert(InputIterator first, InputIterator last);

- Requires: `InputIterator` is a model of Input Iterator over elements of type `value_type`. `first` and `last` are not iterators into any views of the `bimap` to which this view belongs. `last` is reachable from first.
- Effects: `iterator hint = end();` `while(first != last) hint = insert(hint, *first++);`
- Complexity: O(m*H(n+m)), where m is the number of elements in `[first, last)`.
- Exception safety: Basic.

    iterator erase(iterator position);

- Requires: `position` is a valid dereferenceable `iterator` of the view.
- Effects: Deletes the element pointed to by `position`.
- Returns: An `iterator` pointing to the element immediately following the one that was deleted, or `end()` if no such element exists.
- Complexity: O(D(n)).
- Exception safety: nothrow.

    template< class CompatibleKey >
    size_type erase(const CompatibleKey & x);

- Effects: Deletes the elements with key equivalent to `x`.
- Returns: Number of elements deleted.
- Complexity: Average case, O(1 + m*D(n)), worst case O(n + m*D(n)), where m is the number of elements deleted.
- Exception safety: Basic.

    iterator erase(iterator first, iterator last);

- Requires: `[first,last)` is a valid range of the view.
- Effects: Deletes the elements in `[first,last)`.
- Returns: `last`.
- Complexity: O(m*D(n)), where m is the number of elements in `[first,last)`.
- Exception safety: nothrow.

    bool replace(iterator position, const value_type & x);

- Requires: `position` is a valid dereferenceable `iterator` of the view.
- Effects: Assigns the value `x` to the element pointed to by `position` into the `bimap` to which the view belongs if, for the value `x`
  - the view is non-unique OR no other element with equivalent key exists (except possibly `*position`),
  - AND replacing is allowed by all other views of the `bimap`.
- Postconditions: Validity of position is preserved in all cases.
- Returns: `true` if the replacement took place, `false` otherwise.
- Complexity: O(R(n)).
- Exception safety: Strong. If an exception is thrown by some user-provided operation the `bimap` to which the view belongs remains in its original state.

    template< class CompatibleKey >
    bool replace_key(iterator position, const CompatibleKey & x);

- Requires: `position` is a valid dereferenceable iterator of the set view. `CompatibleKey` can be assigned to `key_type`.
- Effects: Assigns the value `x` to `e.first`, where `e` is the element pointed to by `position` into the `bimap` to which the set view belongs if,
  - the map view is non-unique OR no other element with equivalent key exists (except possibly `*position`),
  - AND replacing is allowed by all other views of the `bimap`.
- Postconditions: Validity of position is preserved in all cases.
- Returns: `true` if the replacement took place, `false` otherwise.
- Complexity: O(R(n)).
- Exception safety: Strong. If an exception is thrown by some user-provided operation, the `bimap` to which the set view belongs remains in its original state.

    template< class CompatibleData >
    bool replace_data(iterator position, const CompatibleData & x);

- Requires: `position` is a valid dereferenceable iterator of the set view. `CompatibleKey` can be assigned to `data_type`.
- Effects: Assigns the value `x` to `e.second`, where `e` is the element pointed to by `position` into the `bimap` to which the set view belongs if,
  - the map view is non-unique OR no other element with equivalent key exists (except possibly `*position`),
  - AND replacing is allowed by all other views of the `bimap`.
- Postconditions: Validity of position is preserved in all cases.
- Returns: `true` if the replacement took place, `false` otherwise.
- Complexity: O(R(n)).
- Exception safety: Strong. If an exception is thrown by some user-provided operation, the `bimap` to which the set view belongs remains in its original state.

    template< class KeyModifier >
    bool modify_key(iterator position, KeyModifier mod);

- Requires: `KeyModifier` is a model of Unary Function accepting arguments of type: `key_type&`; `position` is a valid dereferenceable iterator of the view.
- Effects: Calls `mod(e.first)` where e is the element pointed to by position and rearranges `*position` into all the views of the `bimap`. If the rearrangement fails, the element is erased. Rearrangement is successful if
  - the map view is non-unique OR no other element with equivalent key exists,
  - AND rearrangement is allowed by all other views of the `bimap`.
- Postconditions: Validity of `position` is preserved if the operation succeeds.
- Returns: `true` if the operation succeeded, `false` otherwise.
- Complexity: O(M(n)).
- Exception safety: Basic. If an exception is thrown by some user-provided operation (except possibly mod), then the element pointed to by position is erased.
- Note: Only provided for map views.

    template< class DataModifier >
    bool modify_data(iterator position, DataModifier mod);

- Requires: `DataModifier` is a model of Unary Function accepting arguments of type: `data_type&`; `position` is a valid dereferenceable iterator of the view.
- Effects: Calls `mod(e.second)` where e is the element pointed to by position and rearranges `*position` into all the views of the `bimap`. If the rearrangement fails, the element is erased. Rearrangement is successful if
  - the oppositte map view is non-unique OR no other element with equivalent key in that view exists,
  - AND rearrangement is allowed by all other views of the `bimap`.
- Postconditions: Validity of `position` is preserved if the operation succeeds.
- Returns: `true` if the operation succeeded, `false` otherwise.
- Complexity: O(M(n)).
- Exception safety: Basic. If an exception is thrown by some user-provided operation (except possibly mod), then the element pointed to by position is erased.
- Note: Only provided for map views.

##### Lookup

`unordered_[multi]set_of` views provide the full lookup functionality required by unordered associative containers, namely `find`, `count`, and `equal_range`. Additionally, these member functions are templatized to allow for non-standard arguments, so extending the types of search operations allowed. The kind of arguments permissible when invoking the lookup member functions is defined by the following concept.

A type `CompatibleKey` is said to be a compatible key of `(Hash, Pred)` if `(CompatibleKey, Hash, Pred)` is a compatible extension of `(Hash, Pred)`. This implies that `Hash` and `Pred` accept arguments of type `CompatibleKey`, which usually means they have several overloads of their corresponding `operator()` member functions.

    template< class CompatibleKey >
    iterator find(const CompatibleKey & x);

    template< class CompatibleKey >
    const_iterator find(const CompatibleKey & x) const;

- Effects: Returns a pointer to an element whose key is equivalent to `x`, or `end()` if such an element does not exist.
- Complexity: Average case O(1) (constant), worst case O(n).

    template< class CompatibleKey >
    size_type count(const CompatibleKey & x) const;

- Effects: Returns the number of elements with key equivalent to `x`.
- Complexity: Average case O(count(x)), worst case O(n).

    template< class CompatibleKey >
    std::pair<iterator,iterator>
        equal_range(const CompatibleKey & x);

    template< class CompatibleKey >
    std::pair<const_iterator,const_iterator>
        equal_range(const CompatibleKey & x) const;

- Effects: Returns a range containing all elements with keys equivalent to `x` (and only those).
- Complexity: Average case O(count(x)), worst case O(n).

##### at(), info_at() and operator[] - set_of only

    template< class CompatibleKey >
    const data_type & at(const CompatibleKey & k) const;

- Requires: `CompatibleKey` is a compatible key of `key_compare`.
- Effects: Returns the `data_type` reference that is associated with `k`, or throws `std::out_of_range` if such key does not exist.
- Complexity: Average case O(1) (constant), worst case O(n).
- Note: Only provided when `unordered_set_of` is used.

The symmetry of bimap imposes some constraints on `operator[]` and the non constant version of at() that are not found in `std::maps`. Tey are only provided if the other collection type is mutable (`list_of`, `vector_of` and `unconstrained_set_of`).

    template< class CompatibleKey >
    data_type & operator[](const CompatibleKey & k);

- Requires: `CompatibleKey` is a compatible key of `key_compare`.
- Effects: `return insert(value_type(k,data_type()))->second;`
- Complexity: If the insertion is performed O(I(n)), else: Average case O(1) (constant), worst case O(n).
- Note: Only provided when `unordered_set_of` is used and the other collection type is mutable.

    template< class CompatibleKey >
    data_type & at(const CompatibleKey & k);

- Requires: `CompatibleKey` is a compatible key of `key_compare`.
- Effects: Returns the `data_type` reference that is associated with `k`, or throws `std::out_of_range` if such key does not exist.
- Complexity: Average case O(1) (constant), worst case O(n).
- Note: Only provided when `unordered_set_of` is used and the other collection type is mutable.

    template< class CompatibleKey >
    info_type & info_at(const CompatibleKey & k);

    template< class CompatibleKey >
    const info_type & info_at(const CompatibleKey & k) const;

- Requires: `CompatibleKey` is a compatible key of `key_compare`.
- Effects: Returns the `info_type` reference that is associated with `k`, or throws `std::out_of_range` if such key does not exist.
- Complexity: Average case O(1) (constant), worst case O(n).
- Note: Only provided when `unordered_set_of` and `info_hook` are used

##### Hash policy

    void rehash(size_type n);

- Effects: Increases if necessary the number of internal buckets so that `size()/bucket_count()` does not exceed the maximum load factor, and `bucket_count()>=n`.
- Postconditions: Validity of iterators and references to the elements contained is preserved.
- Complexity: Average case O(size()), worst case O(size(n)2).
- Exception safety: Strong.

##### Serialization

Views cannot be serialized on their own, but only as part of the `bimap` into which they are embedded. In describing the additional preconditions and guarantees associated to `unordered_[multi]set_of` views with respect to serialization of their embedding containers, we use the concepts defined in the `bimap` serialization section.

- Requires: No additional requirements to those imposed by the container.

- Requires: Additionally to the general requirements, `key_eq()` must be serialization-compatible with `m.get<i>().key_eq()`, where i is the position of the `unordered_[multi]set_of` view in the container.
- Postconditions: On successful loading, the range `[begin(), end())` contains restored copies of every element in `[m.get<i>().begin(), m.get<i>().end())`, though not necessarily in the same order.

- Requires: `it` is a valid `iterator` of the view. The associated `bimap` has been previously saved.

- Postconditions: On successful loading, if `it` was dereferenceable then `*it`' is the restored copy of `*it`, otherwise `it`'`== end()`.
- Note: It is allowed that `it` be a `const_iterator` and the restored `it`' an `iterator`, or viceversa.

- Requires: `it` is a valid local iterator of the view. The associated `bimap` has been previously saved.

- Postconditions: On successful loading, if `it` was dereferenceable then `*it`' is the restored copy of `*it`; if `it` was `m.get<i>().end(n)` for some n, then `it`'`== m`'`.get<i>().end(n)` (where `b` is the original `bimap`, `b`' its restored copy and `i` is the ordinal of the index.)
- Note: It is allowed that `it` be a `const_local_iterator` and the restored `it`' a `local_iterator`, or viceversa.