Boost.MultiIndex Documentation - Random access indices reference

# Boost.MultiIndex Random access indices reference

Sequenced indices
Boost.MultiIndex reference
Key extraction

## Contents

- Header `"boost/multi_index/random_access_index_fwd.hpp"` synopsis
- Header `"boost/multi_index/random_access_index.hpp"` synopsis
  - `random_access` index specifier
  - Random access indices
    - Complexity signature
    - Instantiation types
    - Nested types
    - Constructors, copy and assignment
    - Iterators
    - Capacity operations
    - Modifiers
    - List operations
    - Rearrange operations
    - Serialization

## Header `"boost/multi_index/random_access_index_fwd.hpp"` synopsis

>     namespace boost{

>     namespace multi_index{

>     // random_access index specifier

>     template<typename TagList=tag<> > struct random_access;

>     // indices

>     namespace detail{

>     template<implementation defined> class index class name implementation defined;

>     } // namespace boost::multi_index::detail

>     } // namespace boost::multi_index

>     } // namespace boost

`random_access_index_fwd.hpp` provides forward declarations for the `random_access` index specifier and its associated random access index class.

## Header `"boost/multi_index/random_access_index.hpp"` synopsis

>     #include <initializer_list>

>     namespace boost{

>     namespace multi_index{

>     // random_access index specifier

>     template<typename TagList=tag<> > struct random_access;

>     // indices

>     namespace detail{

>     template<implementation defined> class index class name implementation defined;

>     // index comparison:

>     // OP is any of ==,<,!=,>,>=,<=

>     template<arg set 1,arg set 2>
>     bool operator OP(
>       const index class name<arg set 1>& x,const index class name<arg set 2>& y);

>     // index specialized algorithms:

>     template<implementation defined>
>     void swap(index class name& x,index class name& y);

>     } // namespace boost::multi_index::detail

>     } // namespace boost::multi_index

>     } // namespace boost

### `random_access` index specifier

This index specifier allows for insertion of a random access index.

>     template<typename TagList=tag<> > struct random_access;

If provided, `TagList` must be an instantiation of `tag`.

### Random access indices

Random access indices are free-order sequences with constant time positional access and random access iterators. Elements in a random access index are by default sorted according to their order of insertion: this means that new elements inserted through a different index of the `multi_index_container` are appended to the end of the random access index; additionally, facilities are provided for further rearrangement of the elements. The public interface of random access indices includes that of sequenced indices, with differences in the complexity of the operations, plus extra operations for positional access (`operator[]` and `at()`) and for capacity handling. Iterators (including to the end of the index) and pointers and references to an element remain valid during the lifetime of the associated container (which can change upon swapping) regardless of the capacity status, or until the referred-to element is erased or extracted; pointers and references to an extracted element, but not so for iterators, become valid again once the element is re-inserted.

Except where noted or if the corresponding interface does not exist, random access indices verify the same container requirements as `std::vector` plus the requirements for `std::list` specific list operations at [list.ops]. Some of the most important differences with respect to `std::vector` are:

- Random access indices do not provide memory contiguity, and hence do not have `data` member functions.
- The complexity of some operations, notably insertion and deletion, differ from those of `std::vector`.
- Unlike as in `std::vector`, insertions into a random access index may fail due to clashings with other indices. This alters the semantics of the operations provided with respect to their analogues in `std::vector`.
- Elements in a random access index are not mutable, and can only be changed in place by means of `replace` and `modify` member functions.
- `push_front` and `pop_front` are provided for compatibility with sequenced indices, even though they take linear time to execute.

>     namespace boost{

>     namespace multi_index{

>     namespace detail{

>     template<implementation defined: dependent on types Value, Allocator, TagList>
>     class name is implementation defined
>     {
>     public:
>       // types:

>       typedef Value                                      value_type;
>       typedef boost::tuples::null_type                   ctor_args;
>       typedef TagList                                    tag_list;
>       typedef Allocator                                  allocator_type;
>       typedef typename allocator_type::reference         reference;
>       typedef typename allocator_type::const_reference   const_reference;
>       typedef implementation defined                     iterator;
>       typedef implementation defined                     const_iterator;
>       typedef implementation defined                     size_type;
>       typedef implementation defined                     difference_type;
>       typedef typename allocator_type::pointer           pointer;
>       typedef typename allocator_type::const_pointer     const_pointer;
>       typedef equivalent to
>         std::reverse_iterator<iterator>                  reverse_iterator;
>       typedef equivalent to
>         std::reverse_iterator<const_iterator>            const_reverse_iterator;
>       typedef same as owning container                   node_type;
>       typedef following [container.insert.return] spec   insert_return_type;

>       // construct/copy/destroy:

>       index class name& operator=(const index class name& x);
>       index class name& operator=(std::initializer_list<value_type> list);

>       template <class InputIterator>
>       void assign(InputIterator first,InputIterator last);
>       void assign(std::initializer_list<value_type> list)
>       void assign(size_type n,const value_type& value);

>       allocator_type get_allocator()const noexcept;

>       // iterators:

>       iterator               begin()noexcept;
>       const_iterator         begin()const noexcept;
>       iterator               end()noexcept;
>       const_iterator         end()const noexcept;
>       reverse_iterator       rbegin()noexcept;
>       const_reverse_iterator rbegin()const noexcept;
>       reverse_iterator       rend()noexcept;
>       const_reverse_iterator rend()const noexcept;
>       const_iterator         cbegin()const noexcept;
>       const_iterator         cend()const noexcept;
>       const_reverse_iterator crbegin()const noexcept;
>       const_reverse_iterator crend()const noexcept;

>       iterator       iterator_to(const value_type& x);
>       const_iterator iterator_to(const value_type& x)const;

>       // capacity:

>       bool      empty()const noexcept;
>       size_type size()const noexcept;
>       size_type max_size()const noexcept;
>       size_type capacity()const noexcept;
>       void      reserve(size_type m);
>       void      shrink_to_fit();

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

>       // access:

>       const_reference operator[](size_type n)const;
>       const_reference at(size_type n)const;
>       const_reference front()const;
>       const_reference back()const;

>       // modifiers:

>       template<typename... Args>
>       std::pair<iterator,bool> emplace_front(Args&&... args);
>       std::pair<iterator,bool> push_front(const value_type& x);
>       std::pair<iterator,bool> push_front(value_type&& x);
>       void                     pop_front();

>       template<typename... Args>
>       std::pair<iterator,bool> emplace_back(Args&&... args);
>       std::pair<iterator,bool> push_back(const value_type& x);
>       std::pair<iterator,bool> push_back(value_type&& x);
>       void                     pop_back();

>       template<typename... Args>
>       std::pair<iterator,bool> emplace(iterator position,Args&&... args);
>       std::pair<iterator,bool> insert(iterator position,const value_type& x);
>       std::pair<iterator,bool> insert(iterator position,value_type&& x);
>       void insert(iterator position,size_type m,const value_type& x);
>       template<typename InputIterator>
>       void insert(iterator position,InputIterator first,InputIterator last);
>       void insert(iterator position,std::initializer_list<value_type> list);
>       insert_return_type insert(const_iterator position,node_type&& nh);

>       node_type extract(const_iterator position);

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

>       bool replace(iterator position,const value_type& x);
>       bool replace(iterator position,value_type&& x);
>       template<typename Modifier> bool modify(iterator position,Modifier mod);
>       template<typename Modifier,typename Rollback>
>       bool modify(iterator position,Modifier mod,Rollback back);

>       void swap(index class name& x);

>       void clear()noexcept;

>       // list operations:

>       template<typename Index> void splice(const_iterator position,Index&& x);
>       template<typename Index>
>       std::pair<iterator,bool> splice(
>         const_iterator position,Index&& x,
>         typename std::remove_reference_t<Index>::const_iterator i);
>       template<typename Index>
>       void splice(
>         const_iterator position,Index&& x,
>         typename std::remove_reference_t<Index>::const_iterator first,
>         typename std::remove_reference_t<Index>::const_iterator last);

>       void remove(const value_type& value);
>       template<typename Predicate> void remove_if(Predicate pred);

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

>       void merge(index class name& x);
>       template <typename Compare> void merge(index class name& x,Compare comp);

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

>       void reverse()noexcept;

>       // rearrange operations:

>       void relocate(iterator position,iterator i);
>       void relocate(iterator position,iterator first,iterator last);
>       template<typename InputIterator> void rearrange(InputIterator first);
>     }

>     // index comparison:

>     template<arg set 1,arg set 2>
>     bool operator==(
>       const index class name<arg set 1>& x,
>       const index class name<arg set 2>& y)
>     {
>       return x.size()==y.size()&&std::equal(x.begin(),x.end(),y.begin());
>     }

>     template<arg set 1,arg set 2>
>     bool operator<(
>       const index class name<arg set 1>& x,
>       const index class name<arg set 2>& y)
>     {
>       return std::lexicographical_compare(x.begin(),x.end(),y.begin(),y.end());
>     }

>     template<arg set 1,arg set 2>
>     bool operator!=(
>       const index class name<arg set 1>& x,
>       const index class name<arg set 2>& y)
>     {
>       return !(x==y);
>     }

>     template<arg set 1,arg set 2>
>     bool operator>(
>       const index class name<arg set 1>& x
>       ,const index class name<arg set 2>& y)
>     {
>       return y<x;
>     }

>     template<arg set 1,arg set 2>
>     bool operator>=(
>       const index class name<arg set 1>& x,
>       const index class name<arg set 2>& y)
>     {
>       return !(x<y);
>     }

>     template<arg set 1,arg set 2>
>     bool operator<=(
>       const index class name<arg set 1>& x,
>       const index class name<arg set 2>& y)
>     {
>       return !(x>y);
>     }

>     // index specialized algorithms:

>     template<implementation defined>
>     void swap(index class name& x,index class name& y);

>     } // namespace boost::multi_index::detail

>     } // namespace boost::multi_index

>     } // namespace boost

#### Complexity signature

Here and in the descriptions of operations of random access indices, we adopt the scheme outlined in the complexity signature section. The complexity signature of random access indices 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

Random access indices are instantiated internally to `multi_index_container` and specified by means of `indexed_by` with the `random_access` index specifier. Instantiations are dependent on the following types:

- `Value` from `multi_index_container`,
- `Allocator` from `multi_index_container`,
- `TagList` from the index specifier (if provided, otherwise `tag<>` is assumed).

`TagList` must be an instantiation of `tag`.

#### Nested types

`iterator
const_iterator`

> These types depend only on `node_type` and the position of the index in the `multi_index_container`.

#### Constructors, copy and assignment

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

`index class name& operator=(const index class name& x);`

> Effects:

> >     a=b;

> where `a` and `b` are the `multi_index_container` objects to which `*this` and `x` belong, respectively.
> Returns: `*this`.

`index class name& operator=(std::initializer_list<value_type> list);`

> Effects:

> >     a=list;

> where `a` is the `multi_index_container` object to which `*this` belongs.
> Returns: `*this`.

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

> Effects:

> >     clear();
> >     insert(end(),first,last);

`void assign(std::initializer_list<value_type> list);`

> Effects:

> >     assign(list.begin(),list.end());

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

> Effects:

> >     clear();
> >     for(size_type i=0;i<n;++n)push_back(v);

#### Iterators

`iterator iterator_to(const value_type& x);
const_iterator iterator_to(const value_type& x)const;`

> Requires: `x` is a reference to an element of the container.
> Returns: An iterator to `x`.
> Complexity: Constant.
> Exception safety: `nothrow`.

#### Capacity operations

`size_type capacity()const noexcept;`

> 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 shrink_to_fit();`

> Effects: Reduces `capacity()` to `size()`.
> 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);
void resize(size_type n,const value_type& x);`

> Requires (first version): `value_type` is `DefaultInsertable` into `multi_index_container`.
> Requires (second version): `value_type` is `CopyInsertable` into `multi_index_container`.
> Effects: If `size()<n`, tries to append `n-size()` default-inserted elements (first version) or copies of `x` (second version) at the end of the index. If `n<size()`, erases the last `size()-n` elements.
> Note: If an expansion is requested, the size of the index is not guaranteed to be `n` after this operation (other indices may ban insertions.)

#### Modifiers

`template<typename... Args>
std::pair<iterator,bool> emplace_front(Args&&... args);`

> Effects:

> >     emplace(begin(),std::forward<Args>(args)...);

> 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.

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

> Effects:

> >     insert(begin(),x);            // lvalue ref version
> >     insert(begin(),std::move(x)); // rvalue ref version

> 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.

`template<typename... Args>
std::pair<iterator,bool> emplace_back(Args&&... args);`

> Effects:

> >     emplace(end(),std::forward<Args>(args)...);

> 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.

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

> Effects:

> >     insert(end(),x);            // lvalue ref version
> >     insert(end(),std::move(x)); // rvalue ref version

> 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.

`template<typename... Args>
std::pair<iterator,bool> emplace(iterator position,Args&&... args);`

> Requires: `value_type` is `EmplaceConstructible` into `multi_index_container` from `args`.
> Effects: Inserts a `value_type` object constructed with `std::forward<Args>(args)...` before `position` if insertion is allowed by all other indices of the `multi_index_container`.
> 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.

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

> Requires (first version): `value_type` is `CopyInsertable` into `multi_index_container`. `position` is a valid iterator of the index.
> Requires (second version): `value_type` is `MoveInsertable` into `multi_index_container`. `position` is a valid iterator of the index.
> Effects: Inserts `x` before `position` if insertion is allowed by all other indices of the `multi_index_container`.
> 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 index.
> Effects:

> >     for(size_type i=0;i<m;++i)insert(position,x);

> Complexity: `O(shl(end()-position,m) + m*I(n+m))`.

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

> Requires: `position` is a valid iterator of the index. `InputIterator` is an input iterator. `value_type` is `EmplaceConstructible` into `multi_index_container` from `*first`. `first` and `last` are not iterators into any index of the `multi_index_container` to which this index belongs. `last` is reachable from `first`.
> Effects: For each element of [`first`, `last`), in this order, inserts it before `position` if insertion is allowed by all other indices of the `multi_index_container`.
> Complexity: `O(shl(end()-position,m) + m*I(n+m))`, where `m` is the number of elements in [`first`,`last`).
> Exception safety: Basic.

`void insert(iterator position,std::initializer_list<value_type> list);`

> Effects:

> >     insert(position,list.begin(),list.end());

`insert_return_type insert(const_iterator position,node_type&& nh);`

> Requires: `nh.empty() || get_allocator()==nh.get_allocator()`.
> Effects: Does nothing if `nh` is empty; otherwise, inserts the node owned by `nh` before `position` if insertion is allowed by all other indices of the `multi_index_container`.
> Postconditions: `nh` is empty.
> Returns: A value `p` of type `insert_return_type`. If `nh` is empty, `p.position` is `end()`, `p.inserted` is `false` and `p.node` is empty; on successful insertion, `p.position` points to the element inserted, `p.inserted` is `true` and `p.node` is empty; if the insertion failed, `p.position` points to an element that caused the insertion to be banned, `p.inserted` is `false` and `p.node` owns the original node. 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. If an exception is thrown, `nh` is not changed.

`node_type extract(const_iterator position);`

> Requires: `position` is a valid dereferenceable iterator of the index.
> Effects: Extracts the node of the element pointed to by `position`.
> Returns: A node handle owning the extracted node.
> Complexity: `O(D(n))`.
> Exception safety: `nothrow`.

`iterator erase(iterator position);`

> Requires: `position` is a valid dereferenceable iterator of the index.
> 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 index.
> 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);`
`bool replace(iterator position,value_type&& x);`

> Requires (first version): `value_type` is `CopyAssignable`. `position` is a valid dereferenceable iterator of the index.
> Requires (second version): `value_type` is `MoveAssignable`. `position` is a valid dereferenceable iterator of the index.
> Effects: Assigns the value `x` to the element pointed to by `position` into the `multi_index_container` to which the index belongs if replacing is allowed by all other indices of the `multi_index_container`.
> 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 `multi_index_container` to which the index belongs remains in its original state.

`template<typename Modifier> bool modify(iterator position,Modifier mod);`

> Requires: `mod` is a unary function object accepting arguments of type `value_type&`. `position` is a valid dereferenceable iterator of the index. The execution of `mod(e)`, where `e` is the element pointed to by `position`, does not invoke any operation of the `multi_index_container` after `e` is directly modified or, before modification, if the operation would invalidate `position`.
> Effects: Calls `mod(e)` where `e` is the element pointed to by `position` and rearranges `*position` into all the indices of the `multi_index_container`. Rearrangement on sequenced indices does not change the position of the element with respect to the index; rearrangement on other indices may or might not succeed. If the rearrangement fails, the element is erased.
> 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 (including `mod`), then the element pointed to by `position` is erased.

`template<typename Modifier,typename Rollback>
bool modify(iterator position,Modifier mod,Rollback back);`

> Requires: `mod` and `back` are unary function objects accepting arguments of type `value_type&`. `position` is a valid dereferenceable iterator of the index. The execution of `mod(e)`, where `e` is the element pointed to by `position`, does not invoke any operation of the `multi_index_container` after `e` is directly modified or, before modification, if the operation would invalidate `position`. `back(e)` does not invoke any operation of the `multi_index_container`.
> Effects: Calls `mod(e)` where `e` is the element pointed to by `position` and tries to rearrange `*position` into all the indices of the `multi_index_container`. Rearrangement on sequenced indices does not change the position of the element with respect to the index; rearrangement on other indices may or might not succeed. If the rearrangement fails, `back(e)` is invoked: if the resulting value of `e` is consistent with its original position and constraints in all indices, the element is kept, otherwise it is erased.
> Postconditions: Validity of `position` is preserved except if the element is erased under the conditions described below.
> Returns: `true` if the operation succeeded, `false` otherwise.
> Complexity: `O(M(n))`.
> Exception safety: Strong, except if `mod` or `back` throw an exception or `back(e)` fails to properly restore the element or there is a throwing user-provided operation after invoking `back(e)`, in which cases the modified element is erased. If `back` throws inside the handling code executing after some other user-provided operation has thrown, it is the exception generated by `back` that is rethrown.

#### List operations

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

`template<typename Index> void splice(const_iterator position,Index&& x);`

> Requires: `x` is a non-const reference to an index of a node-compatible `multi_index_container`. `position` is a valid iterator of the index, and must be exactly `end()` if the source and destination containers are the same.
> Effects:

> >     splice(position,x,x.begin(),x.end());

`template<typename Index> std::pair<iterator,bool> splice(
const_iterator position,Index&& x,
typename std::remove_reference_t<Index>::const_iterator i);`

> Requires: `x` is a non-const reference to an index of a node-compatible `multi_index_container`. If `get_allocator()!=x.get_allocator()`, `value_type` must be `CopyInsertable` into the destination `multi_index_container`. `position` is a valid iterator of the index. `i` is a valid dereferenceable iterator of `x`.
> Effects:
> - (Same container) if the source and destination containers are the same, repositions the element pointed to by `i` before `position` unless both iterators refer to the same element.
> - (Transfer splice) else, if `get_allocator()==x.get_allocator()`, transfers the node of the element referred to by `i` into the destination `multi_index_container` right before `position` if insertion is allowed by all other indices of the `multi_index_container`.
> - (Destructive splice) else, insertion of `*i` is tried before `position`; if the operation is successful, the element is erased from `x`.
> Postconditions: If transfer succeeds, for any index in the source container having the same `iterator`/`const_iterator` types as the corresponding index in the destination container, iterators referring to `*i` remain valid and behave as iterators of the destination index.
> Returns: The return value is a pair `p`. `p.second` is `true` if and only if insertion (either through transfer or copy insertion) took place or the source and destination containers are the same. If `p.second` is `true`, `p.first` points to the inserted element or to `*i` if the source and destination containers are the same; 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: If the source and destination containers are the same, `O(rel(position,i',i'+1))`, where `i'` is the projection of `i` into the index of `position`; otherwise, `O(shl(end()-position,1) + I(n) + D(x.size()))`.
> Exception safety: If the source and destination containers are the same, `nothrow`; otherwise strong.
> Implementation note: The destructive variant of this operation is provided for reasons of backwards compatibility with previous versions of this library where allocator equality was not required.

`template<typename Index> void splice(
const_iterator position,Index&& x,
typename std::remove_reference_t<Index>::const_iterator first,
typename std::remove_reference_t<Index>::const_iterator last);`

> Requires: `x` is a non-const reference to an index of a node-compatible `multi_index_container`. If `get_allocator()!=x.get_allocator()`, `value_type` must be `CopyInsertable` into the destination `multi_index_container`. `position` is a valid iterator of the index and does not point to any element in [`first`,`last`). [`first`,`last`) is a valid range of `x`.
> Effects:
> - (Same container) if the source and destination containers are the same, repositions all the elements of [`first`,`last`), in this order, before `position`.
> - (Transfer splice) else, if `get_allocator()==x.get_allocator()`, then, for each node in [`first`,`last`), in this order, the node is transferred to the `multi_index_container` right before `position` if insertion is allowed by all other indices of the `multi_index_container`.
> - (Destructive splice) else, for each element in [`first`,`last`), in this order, insertion is tried before `position`; if the operation is successful, the element is erased from `x`.
> Postconditions: For any index in the source container having the same `iterator`/`const_iterator` types as the corresponding index in the destination container, iterators referring to the transferred elements remain valid and behave as iterators of the destination index.
> Complexity: If `&x==this`, `O(rel(position,first,last))`; else, if the source and destination containers are the same, `O(n)`; otherwise, `O(shl(end()-position,m) + m*(I(n+m) + D(x.size())))`, where `m` is the number of elements in [`first`,`last`).
> Exception safety: If the source and destination containers are the same, `nothrow`; otherwise basic.
> Implementation note: The destructive variant of this operation is provided for reasons of backwards compatibility with previous versions of this library where allocator equality was not required.

`void remove(const value_type& value);`

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

`template<typename Predicate> void remove_if(Predicate pred);`

> Effects: Erases all elements `x` of the index 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(index class name& x);`

> Requires: Either `get_allocator()==x.get_allocator()` or `value_type` is `CopyInsertable` into the `multi_index_container`. `std::less<value_type>` induces a strict weak ordering over `value_type`. Both the index and `x` are sorted according to `std::less<value_type>`.
> Effects: Attempts to splice every element of `x` into the corresponding position of the index (according to the order). 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 index and remaining elements in `x` are sorted. Validity of iterators and references is preserved, except to elements removed from `x` if `get_allocator()!=x.get_allocator()`.
> 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 <typename Compare> void merge(index class name& x,Compare comp);`

> Requires: Either `get_allocator()==x.get_allocator()` or `value_type` is `CopyInsertable` into the `multi_index_container`. `Compare` induces a strict weak ordering over `value_type`. Both the index and `x` are sorted according to `comp`.
> Effects: Attempts to splice every element of `x` into the corresponding position of the index (according to `comp`). 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 index and remaining elements in `x` are sorted according to `comp`. Validity of iterators and references is preserved, except to elements removed from `x` if `get_allocator()!=x.get_allocator()`.
> 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>` induces a strict weark ordering over `value_type`.
> Effects: Sorts the index 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 <typename Compare> void sort(Compare comp);`

> Requires: `Compare` induces a strict weak ordering over `value_type`.
> Effects: Sorts the index 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()noexcept;`

> Effects: Reverses the order of the elements in the index.
> Postconditions: Validity of iterators and references is preserved.
> Complexity: `O(n)`.

#### Rearrange operations

These operations, without counterpart in STL sequence containers (although `std::list::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 index. `i` is a valid dereferenceable iterator of the index.
> 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: `O(rel(position,i,i+1))`.
> Exception safety: `nothrow`.

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

> Requires: `position` is a valid iterator of the index. `first` and `last` are valid iterators of the index. `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: `O(rel(position,first,last))`.
> Exception safety: `nothrow`.

`template<typename InputIterator> void rearrange(InputIterator first);`

> Requires: The range [`first`, `std::advance(first,n)`), where `n` is the size of the index, is a free view of the index.
> Effects: The elements are rearranged so as to match the order of the previously described view.
> Postconditions: No iterator or reference is invalidated.
> Complexity: `O(n)`.
> Exception safety: Basic.

#### Serialization

Indices cannot be serialized on their own, but only as part of the `multi_index_container` into which they are embedded. In describing the additional preconditions and guarantees associated to random access indices with respect to serialization of their embedding containers, we use the concepts defined in the `multi_index_container` serialization section.

Operation: saving of a `multi_index_container` `m` to an output archive (XML archive) `ar`.

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

Operation: loading of a `multi_index_container` `m'` 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 random access index 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 index. The associated `multi_index_container` 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.

Sequenced indices
Boost.MultiIndex reference
Key extraction

Revised August 30th 2021

© Copyright 2003-2021 Joaquín M López Muñoz. Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)