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### vector_of Reference

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

    namespace boost {
    namespace bimaps {

    template< class KeyType >
    struct vector_of;

    struct vector_of_relation;

    } // namespace bimap
    } // namespace boost

#### vector_of views

vector_of views are free-order sequences with constant time positional access and random access iterators. Elements in a vector_of view are by default sorted according to their order of insertion: this means that new elements inserted through a different view of the `bimap` are appended to the end of the vector_of view; additionally, facilities are provided for further rearrangement of the elements. The public interface of vector_of views includes that of list_of views, with differences in the complexity of the operations, plus extra operations for positional access (`operator[]` and `at()`) and for capacity handling. Validity of iterators and references to elements is preserved in all operations, regardless of the capacity status.

As is the case with list_of views, vector_of views have the following limitations with respect to STL sequence containers:

- vector_of views are not Assignable (like any other view.)
- Insertions into a vector_of view may fail due to clashings with other views. This alters the semantics of the operations provided with respect to their analogues in STL sequence containers.
- Elements in a vector_of view are not mutable, and can only be changed by means of replace and modify member functions.

Having these restrictions into account, vector of views are models of Random Access Container and Back Insertion Sequence. Although these views do not model Front Insertion Sequence, because front insertion and deletion take linear time, front operations are nonetheless provided to match the interface of list_of views. We only describe those types and operations that are either not present in the concepts modeled or do not exactly conform to the requirements for these types of containers.

    namespace boost {
    namespace bimaps {
    namespace views {

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

        // types

        typedef -unspecified- value_type;
        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- reverse_iterator;
        typedef -unspecified- const_reverse_iterator;

        typedef -unspecified- info_type;

        // construct / copy / destroy

        this_type & operator=(this_type & x);

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

        void assign(size_type n, const value_type & value);

        allocator_type get_allocator() const;

        // iterators

        iterator               begin();
        const_iterator         begin() const;

        iterator               end();
        const_iterator         end() const;

        reverse_iterator       rbegin();
        const_reverse_iterator rbegin() const;

        reverse_iterator       rend();
        const_reverse_iterator rend() const;

        // capacity

        bool      empty() const;

        size_type size() const;

        size_type max_size() const;

        size_type capacity() const;

        void reserve(size_type m);

        void resize(size_type n, const value_type & x = value_type());

        // access

        const_reference operator[](size_type n) const;

        const_reference at(size_type n) const;

        const_reference front() const;

        const_reference back() const;

        // modifiers

        std::pair<iterator,bool> push_front(const value_type & x);
        void                     pop_front();

        std::pair<iterator,bool> push_back(const value_type & x);
        void                     pop_back();

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

        void insert(iterator position, size_type m, const value_type & x);

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

        iterator erase(iterator position);
        iterator erase(iterator first, iterator last);

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

        // Only in map views
        // {
          typedef -unspecified- key_type;
          typedef -unspecified- mapped_type;
          typedef -unspecified- data_type; // Equal to mapped_type

          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();

        // list operations

        void splice(iterator position, this_type & x);
        void splice(iterator position, this_type & x, iterator i);
        void splice(
            iterator position, this_type & x, iterator first, iterator last);

        void remove(const value_type & value);

        template< class Predicate >
        void remove_if(Predicate pred);

        void unique();

        template< class BinaryPredicate >
        void unique(BinaryPredicate binary_pred);

        void merge(this_type & x);

        template< typename Compare >
        void merge(this_type & x, Compare comp);

        void sort();

        template< typename Compare >
        void sort(Compare comp);

        void reverse();

        // rearrange operations

        void relocate(iterator position, iterator i);
        void relocate(iterator position, iterator first, iterator last);
    };

    // view comparison

    bool operator==(const this_type & v1, const this_type & v2 );
    bool operator< (const this_type & v1, const this_type & v2 );
    bool operator!=(const this_type & v1, const this_type & v2 );
    bool operator> (const this_type & v1, const this_type & v2 );
    bool operator>=(const this_type & v1, const this_type & v2 );
    bool operator<=(const this_type & v1, const this_type & v2 );

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

In the case of a `bimap< vector_of<Left>, ... >`

In the set view:

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

In the left map view:

    typedef  Left  key_type;
    typedef  ...   mapped_type;

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

In the right map view:

    typedef  ...  key_type;
    typedef  Left mapped_type;

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

##### Complexity signature

Here and in the descriptions of operations of `vector_of` views, we adopt the scheme outlined in the complexity signature section. The complexity signature of `vector_of` view is:

- copying: `c(n) = n * log(n)`,
- insertion: `i(n) = 1` (amortized constant),
- hinted insertion: `h(n) = 1` (amortized constant),
- deletion: `d(n) = m`, where m is the distance from the deleted element to the end of the sequence,
- replacement: `r(n) = 1` (constant),
- modifying: `m(n) = 1` (constant).

The following expressions are also used as a convenience for writing down some of the complexity formulas:

`shl(a,b) = a+b` if a is nonzero, 0 otherwise. `rel(a,b,c) =` if `a<b`, `c-a`, else `a-b`,

(`shl` and `rel` stand for shift left and relocate, respectively.)

##### Instantiation types

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

- `Value` from `vector_of`,
- `Allocator` from `bimap`,

##### Constructors, copy and assignment

As explained in the views concepts section, views do not have public constructors or destructors. Assignment, on the other hand, is provided.

    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`.

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

- Requires: `InputIterator` is a model of Input Iterator over elements of type `value_type` or a type convertible to `value_type`. `first` and `last` are not iterators into any view of the `bimap` to which this view belongs. `last` is reachable from `first`.
- Effects: `clear(); insert(end(),first,last);`

    void assign(size_type n, const value_type & value);

- Effects: `clear(); for(size_type i = 0; i < n; ++n) push_back(v);`

##### Capacity operations

    size_type capacity() const;

- Returns: The total number of elements `c` such that, when `size() < c`, back insertions happen in constant time (the general case as described by i(n) is amortized constant time.)
- Note: Validity of iterators and references to elements is preserved in all insertions, regardless of the capacity status.

    void reserve(size_type m);

- Effects: If the previous value of `capacity()` was greater than or equal to `m`, nothing is done; otherwise, the internal capacity is changed so that `capacity()>=m`.
- Complexity: If the capacity is not changed, constant; otherwise O(n).
- Exception safety: If the capacity is not changed, nothrow; otherwise, strong.

    void resize(size_type n, const value_type & x = value_type());

- Effects: `if( n > size() ) insert(end(), n-size(), x);` `else if( n<size() ) erase(begin()+n,end());`
- Note: If an expansion is requested, the size of the view is not guaranteed to be n after this operation (other views may ban insertions.)

##### Modifiers

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

- Effects: Inserts x at the beginning of the sequence if no other view of the `bimap` bans the insertion.
- 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(n+I(n)).
- Exception safety: Strong.

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

- Effects: Inserts `x` at the end of the sequence if no other view of the `bimap` bans the insertion.
- 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.

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

- Requires: `position` is a valid iterator of the view.
- Effects: Inserts `x` before position if 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(shl(end()-position,1) + I(n)).
- Exception safety: Strong.

    void insert(iterator position, size_type m, const value_type & x);

- Requires: `position` is a valid iterator of the view.
- Effects: `for(size_type i = 0; i < m; ++i) insert(position, x);`
- Complexity: O(shl(end()-position,m) + m*I(n+m)).

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

- Requires: `position` is a valid iterator of the view. `InputIterator` is a model of Input Iterator over elements of type `value_type` or a type convertible to `value_type`. `first` and `last` are not iterators into any view of the `bimap` to which this view belongs. `last` is reachable from `first`.
- Effects: `while(first!=last)insert(position,*first++);`
- Complexity: O(shl(end()-position,m) + m*I(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.

    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 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 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 `mapped_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 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. It is successful if the 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: `mapped_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. It is successful if the 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.

##### List operations

`vector_of` views replicate the interface of `list_of` views, which in turn includes the list operations provided by `std::list`. The syntax and behavior of these operations exactly matches those of `list_of` views, but the associated complexity bounds differ in general.

    void splice(iterator position, this_type & x);

- Requires: `position` is a valid iterator of the view. `&x!=this`.
- Effects: Inserts the contents of `x` before position, in the same order as they were in `x`. Those elements successfully inserted are erased from `x`.
- Complexity: O(shl(end()-position,x.size()) + x.size()*I(n+x.size()) + x.size()*D(x.size())).
- Exception safety: Basic.

    void splice(iterator position, this_type & x,iterator i);

- Requires: `position` is a valid iterator of the view. `i` is a valid dereferenceable iterator `x`.
- Effects: Inserts the element pointed to by `i` before `position`: if insertion is successful, the element is erased from `x`. In the special case `&x==this`, no copy or deletion is performed, and the operation is always successful. If `position==i`, no operation is performed.
- Postconditions: If `&x==this`, no iterator or reference is invalidated.
- Complexity: If `&x==this`, O(rel(position,i,i+1)); otherwise O(shl(end()-position,1) + I(n) + D(n)).
- Exception safety: If `&x==this`, nothrow; otherwise, strong.

    void splice(iterator position, this_type & x, iterator first, iterator last);

- Requires: `position` is a valid iterator of the view. `first` and `last` are valid iterators of `x`. `last` is reachable from `first`. `position` is not in the range `[first,last)`.
- Effects: For each element in the range `[first,last)`, insertion is tried before `position`; if the operation is successful, the element is erased from `x`. In the special case `&x==this`, no copy or deletion is performed, and insertions are always successful.
- Postconditions: If `&x==this`, no iterator or reference is invalidated.
- Complexity: If `&x==this`, O(rel(position,first,last)); otherwise O(shl(end()-position,m) + m*I(n+m) + m*D(x.size())) where m is the number of elements in `[first,last)`.
- Exception safety: If `&x==this`, nothrow; otherwise, basic.

    void remove(const value_type & value);

- Effects: Erases all elements of the view which compare equal to `value`.
- Complexity: O(n + m*D(n)), where m is the number of elements erased.
- Exception safety: Basic.

    template< class Predicate >
    void remove_if(Predicate pred);

- Effects: Erases all elements `x` of the view for which `pred(x)` holds.
- Complexity: O(n + m*D(n)), where m is the number of elements erased.
- Exception safety: Basic.

    void unique();

- Effects: Eliminates all but the first element from every consecutive group of equal elements referred to by the iterator `i` in the range `[first+1,last)` for which `*i==*(i-1)`.
- Complexity: O(n + m*D(n)), where m is the number of elements erased.
- Exception safety: Basic.

    template< class BinaryPredicate >
    void unique(BinaryPredicate binary_pred);

- Effects: Eliminates all but the first element from every consecutive group of elements referred to by the iterator i in the range `[first+1,last)` for which `binary_pred(*i, *(i-1))` holds.
- Complexity: O(n + m*D(n)), where m is the number of elements erased.
- Exception safety: Basic.

    void merge(this_type & x);

- Requires: `std::less<value_type>` is a Strict Weak Ordering over `value_type`. Both the view and `x` are sorted according to `std::less<value_type>`.
- Effects: Attempts to insert every element of x into the corresponding position of the view (according to the order). Elements successfully inserted are erased from `x`. The resulting sequence is stable, i.e. equivalent elements of either container preserve their relative position. In the special case `&x==this`, no operation is performed.
- Postconditions: Elements in the view and remaining elements in `x` are sorted. Validity of iterators to the view and of non-erased elements of `x` references is preserved.
- Complexity: If `&x==this`, constant; otherwise O(n + x.size()*I(n+x.size()) + x.size()*D(x.size())).
- Exception safety: If `&x==this`, nothrow; otherwise, basic.

    template< class Compare >
    void merge(this_type & x, Compare comp);

- Requires: `Compare` is a Strict Weak Ordering over `value_type`. Both the view and `x` are sorted according to comp.
- Effects: Attempts to insert every element of `x` into the corresponding position of the view (according to `comp`). Elements successfully inserted are erased from `x`. The resulting sequence is stable, i.e. equivalent elements of either container preserve their relative position. In the special case `&x==this`, no operation is performed.
- Postconditions: Elements in the view and remaining elements in `x` are sorted according to `comp`. Validity of iterators to the view and of non-erased elements of `x` references is preserved.
- Complexity: If `&x==this`, constant; otherwise O(n + x.size()*I(n+x.size()) + x.size()*D(x.size())).
- Exception safety: If `&x==this`, nothrow; otherwise, basic.

    void sort();

- Requires: `std::less<value_type>` is a Strict Weak Ordering over `value_type`.
- Effects: Sorts the view according to `std::less<value_type>`. The sorting is stable, i.e. equivalent elements preserve their relative position.
- Postconditions: Validity of iterators and references is preserved.
- Complexity: O(n*log(n)).
- Exception safety: Basic.

    template< class Compare >
    void sort(Compare comp);

- Requires: Compare is a Strict Weak Ordering over `value_type`.
- Effects: Sorts the view according to `comp`. The sorting is stable, i.e. equivalent elements preserve their relative position.
- Postconditions: Validity of iterators and references is preserved.
- Complexity: O(n*log(n)).
- Exception safety: Basic.

    void reverse();

- Effects: Reverses the order of the elements in the view.
- Postconditions: Validity of iterators and references is preserved.
- Complexity: O(n).
- Exception safety: nothrow.

##### Rearrange operations

These operations, without counterpart in `std::list` (although splice provides partially overlapping functionality), perform individual and global repositioning of elements inside the index.

    void relocate(iterator position, iterator i);

- Requires: `position` is a valid iterator of the view. `i` is a valid dereferenceable iterator of the view.
- Effects: Inserts the element pointed to by `i` before `position`. If `position==i`, no operation is performed.
- Postconditions: No iterator or reference is invalidated.
- Complexity: Constant.
- Exception safety: nothrow.

    void relocate(iterator position, iterator first, iterator last);

- Requires: `position` is a valid iterator of the view. `first` and `last` are valid iterators of the view. `last` is reachable from `first`. `position` is not in the range `[first,last)`.
- Effects: The range of elements `[first,last)` is repositioned just before `position`.
- Postconditions: No iterator or reference is invalidated.
- Complexity: Constant.
- Exception safety: nothrow.

##### 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 `vector_of` views with respect to serialization of their embedding containers, we use the concepts defined in the `bimap` serialization section.

Operation: saving of a `bimap` b to an output archive (XML archive) ar.

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

Operation: loading of a `bimap` b' from an input archive (XML archive) ar.

- Requires: No additional requirements to those imposed by the container.
- Postconditions: On successful loading, each of the elements of `[begin(), end())` is a restored copy of the corresponding element in `[m.get<i>().begin(), m.get<i>().end())`, where `i` is the position of the `vector_of` view in the container.

Operation: saving of an `iterator` or `const_iterator` `it` to an output archive (XML archive) ar.

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

Operation: loading of an `iterator` or `const_iterator` `it`' from an input archive (XML archive) ar.

- 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.