Boost.MultiIndex Ordered indices reference

Contents

• Header "boost/multi_index/ordered_index_fwd.hpp" synopsis
• Header "boost/multi_index/ordered_index.hpp" synopsis
  • Index specifiers ordered_unique and ordered_non_unique
  • Ordered indices
    • Complexity signature
    • Instantiation types
    • Constructors, copy and assignment
    • Modifiers
    • Observers
    • Set operations
    • Range operations
    • Serialization

Header "boost/multi_index/ordered_index_fwd.hpp" synopsis

namespace boost{

namespace multi_index{

// index specifiers ordered_unique and ordered_non_unique

template<consult ordered_unique reference for arguments>
struct ordered_unique;
template<consult ordered_non_unique reference for arguments>
struct ordered_non_unique;

// indices

namespace detail{

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

} // namespace boost::multi_index::detail

} // namespace boost::multi_index 

} // namespace boost

ordered_index_fwd.hpp provides forward declarations for index specifiers ordered_unique and ordered_non_unique and their associated ordered index classes.

Header "boost/multi_index/ordered_index.hpp" synopsis

namespace boost{

namespace multi_index{

// index specifiers ordered_unique and ordered_non_unique

template<consult ordered_unique reference for arguments>
struct ordered_unique;
template<consult ordered_non_unique reference for arguments>
struct ordered_non_unique;

// 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

Index specifiers ordered_unique and ordered_non_unique

These index specifiers allow for insertion of ordered indices without and with allowance of duplicate elements, respectively. The syntax of ordered_unique and ordered_non_unique coincide, thus describe them in a grouped manner. ordered_unique and ordered_non_unique can be instantiated in two different forms, according to whether a tag list for the index is provided or not:

template<
  typename KeyFromValue,
  typename Compare=std::less<KeyFromValue::result_type>
>
struct (ordered_unique | ordered_non_unique);

template<
  typename TagList,
  typename KeyFromValue,
  typename Compare=std::less<KeyFromValue::result_type>
>
struct (ordered_unique | ordered_non_unique);

If provided, TagList must be an instantiation of the class template tag. The template arguments are used by the corresponding index implementation, refer to the ordered indices reference section for further explanations on their acceptable type values.

Ordered indices

An ordered index provides a set-like interface to the underlying heap of elements contained in a multi_index_container. An ordered index is particularized according to a given Key Extractor that retrieves keys from elements of multi_index_container and a comparison predicate.

There are two variants of ordered indices: unique, which do not allow duplicate elements (with respect to its associated comparison predicate) and non-unique, which accept those duplicates. The interface of these two variants is the same, so they are documented together, with minor differences explicitly stated when they exist.

Except where noted, ordered indices (both unique and non-unique) are models of Sorted Associative Container and Unique Associative Container, much as std::sets are. Accordingly, validity of iterators and references to elements is preserved. 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 these types of containers.

namespace boost{

namespace multi_index{

namespace{ implementation defined unbounded; } // see range()

namespace detail{

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

  typedef typename KeyFromValue::result_type         key_type;
  typedef Value                                      value_type;
  typedef KeyFromValue                               key_from_value;
  typedef Compare                                    key_compare;
  typedef implementation defined                     value_compare;
  typedef tuple<key_from_value,key_compare>          ctor_args;
  typedef Allocator                                  allocator_type;
  typedef typename Allocator::reference              reference;
  typedef typename Allocator::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::pointer                pointer;
  typedef typename Allocator::const_pointer          const_pointer;
  typedef equivalent to
    std::reverse_iterator<iterator>                  reverse_iterator;
  typedef equivalent to
    std::reverse_iterator<const_iterator>            const_reverse_iterator;

  // construct/copy/destroy:

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

  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;

  // modifiers:

  std::pair<iterator,bool> insert(const value_type& x);
  iterator insert(iterator position,const value_type& x);
  template<typename InputIterator>
  void insert(InputIterator first,InputIterator last);

  iterator  erase(iterator position);
  size_type erase(const key_type& x);
  iterator  erase(iterator first,iterator last);

  bool replace(iterator position,const value_type& x);
  template<typename Modifier> bool modify(iterator position,Modifier mod);
  template<typename Modifier> bool modify_key(iterator position,Modifier mod);
  
  void swap(index class name& x);
  void clear();

  // observers:

  key_from_value key_extractor()const;
  key_compare    key_comp()const;
  value_compare  value_comp()const;

  // set operations:

  template<typename CompatibleKey>
  iterator find(const CompatibleKey& x)const;
  template<typename CompatibleKey,typename CompatibleCompare>
  iterator find(
    const CompatibleKey& x,const CompatibleCompare& comp)const;

  template<typename CompatibleKey>
  size_type count(const CompatibleKey& x)const;
  template<typename CompatibleKey,typename CompatibleCompare>
  size_type count(const CompatibleKey& x,const CompatibleCompare& comp)const;

  template<typename CompatibleKey>
  iterator lower_bound(const CompatibleKey& x)const;
  template<typename CompatibleKey,typename CompatibleCompare>
  iterator lower_bound(
    const CompatibleKey& x,const CompatibleCompare& comp)const;

  template<typename CompatibleKey>
  iterator upper_bound(const CompatibleKey& x)const;
  template<typename CompatibleKey,typename CompatibleCompare>
  iterator upper_bound(
    const CompatibleKey& x,const CompatibleCompare& comp)const;

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

  // range:

  template<typename LowerBounder,typename UpperBounder>
  std::pair<iterator,iterator> range(
    LowerBounder lower,UpperBounder upper)const;
};

// 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 ordered indices, we adopt the scheme outlined in the complexity signature section. The complexity signature of ordered indices is:

• copying: c(n)=n*log(n),
• insertion: i(n)=log(n),
• hinted insertion: h(n)=1 (constant) if the hint element precedes the point of insertion, h(n)=log(n) otherwise,
• deletion: d(n)=1 (amortized constant),
• replacement: r(n)=1 (constant) if the element position does not change, r(n)=log(n) otherwise,
• modifying: m(n)=1 (constant) if the element position does not change, m(n)=log(n) otherwise.

Instantiation types

Ordered indices are instantiated internally to multi_index_container and specified by means of indexed_by with index specifiers ordered_unique and ordered_non_unique. Instantiations are dependent on the following types:

• Value from multi_index_container,
• Allocator from multi_index_container,
• TagList from the index specifier (if provided),
• KeyFromValue from the index specifier,
• Compare from the index specifier.

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.

Effects:

a=b;

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

Modifiers

Effects: Inserts x into the multi_index_container to which the index belongs if

• the index is non-unique OR no other element exists with equivalent key,
• AND 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(I(n)).
Exception safety: Strong.

Requires: position is a valid iterator of the index. Effects: Inserts x into the multi_index_container to which the index belongs if

• the index is non-unique OR no other element exists with equivalent key,
• AND insertion is allowed by all other indices of the multi_index_container.

position is used as a hint to improve the efficiency of the operation.
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.

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 index of the multi_index_container to which this index 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.

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.

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

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

Requires: 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, for the value x

• the index is non-unique OR no other element exists (except possibly *position) with equivalent key,
• AND 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.

Requires: Modifier is a model of Unary Function accepting arguments of type value_type&. position is a valid dereferenceable iterator of the index. 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 is successful if

• the index is non-unique OR no other element exists with equivalent key,
• AND rearrangement is allowed by all other indices of the multi_index_container.

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 (except possibly mod), then the element pointed to by position is erased.

Requires: key_from_value is a read/write Key Extractor from value_type. Modifier is a model of Unary Function accepting arguments of type key_type&. position is a valid dereferenceable iterator of the index. Effects: Calls mod(k) where k is the key obtained by the internal KeyFromValue object of the index from the element pointed to by position, and rearranges *position into all the indices of the multi_index_container. Rearrangement is successful if

• the index is non-unique OR no other element exists with equivalent key,
• AND rearrangement is allowed by all other indices of the multi_index_container.

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 (except possibly mod), then the element pointed to by position is erased.

Observers

Apart from standard key_comp and value_comp, ordered indices have a member function for retrieving the internal key extractor used.

Returns a copy of the key_from_value object used to construct the index.
Complexity: Constant.

Set operations

Ordered indices provide the full lookup functionality required by Sorted Associative Containers and Unique Associative Containers, namely find, count, lower_bound, upper_bound 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.

Consider a Strict Weak Ordering Compare over values of type Key. A pair of types (CompatibleKey, CompatibleCompare) is said to be a compatible extension of Compare if

1. CompatibleCompare is a Binary Predicate over (Key, CompatibleKey),
2. CompatibleCompare is a Binary Predicate over (CompatibleKey, Key),
3. if c_comp(ck,k1) then !c_comp(k1,ck),
4. if !c_comp(ck,k1) and !comp(k1,k2) then !c_comp(ck,k2),
5. if !c_comp(k1,ck) and !comp(k2,k1) then !c_comp(k2,ck),

Additionally, a type CompatibleKey is said to be a compatible key of Compare if (CompatibleKey, Compare) is a compatible extension of Compare. This implies that Compare, as well as being a strict weak ordering, accepts arguments of type CompatibleKey, which usually means it has several overloads of operator().

In the context of a compatible extension or a compatible key, the expressions "equivalent", "less than" and "greater than" take on their obvious interpretations.

Requires: CompatibleKey is a compatible key of key_compare. Effects: Returns a pointer to an element whose key is equivalent to x, or end() if such an element does not exist.
Complexity: O(log(n)).

Requires: (CompatibleKey, CompatibleCompare) is a compatible extension of key_compare. Effects: Returns a pointer to an element whose key is equivalent to x, or end() if such an element does not exist.
Complexity: O(log(n)).

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

Requires: CompatibleKey is a compatible key of key_compare. Effects: Returns the number of elements with key equivalent to x.
Complexity: O(log(n) + count(x)).

Requires: (CompatibleKey, CompatibleCompare) is a compatible extension of key_compare. Effects: Returns the number of elements with key equivalent to x.
Complexity: O(log(n) + count(x,comp)).

Requires: CompatibleKey is a compatible key of key_compare. Effects: Returns an iterator pointing to the first element with key not less than x, or end() if such an element does not exist.
Complexity: O(log(n)).

Requires: (CompatibleKey, CompatibleCompare) is a compatible extension of key_compare. Effects: Returns an iterator pointing to the first element with key not less than x, or end() if such an element does not exist.
Complexity: O(log(n)).

Requires: CompatibleKey is a compatible key of key_compare. Effects: Returns an iterator pointing to the first element with key greater than x, or end() if such an element does not exist.
Complexity: O(log(n)).

Requires: (CompatibleKey, CompatibleCompare) is a compatible extension of key_compare. Effects: Returns an iterator pointing to the first element with key greater than x, or end() if such an element does not exist.
Complexity: O(log(n)).

Requires: CompatibleKey is a compatible key of key_compare. Effects: Equivalent to make_pair(lower_bound(x),upper_bound(x)).
Complexity: O(log(n)).

Requires: (CompatibleKey, CompatibleCompare) is a compatible extension of key_compare. Effects: Equivalent to make_pair(lower_bound(x,comp),upper_bound(x,comp)).
Complexity: O(log(n)).

Range operations

The member function range is not defined for sorted associative containers, but ordered indices provide it as a convenient utility. A range or interval is defined by two conditions for the lower and upper bounds, which are modeled after the following concepts.

Consider a Strict Weak Ordering Compare over values of type Key. A type LowerBounder is said to be a lower bounder of Compare if

1. LowerBounder is a Predicate over Key,
2. if lower(k1) and !comp(k2,k1) then lower(k2),

1. UpperBounder is a Predicate over Key,
2. if upper(k1) and !comp(k1,k2) then upper(k2),

Requires: LowerBounder and UpperBounder are a lower and upper bounder of key_compare, respectively. Effects: Returns a pair of iterators pointing to the beginning and one past the end of the subsequence of elements satisfying lower and upper simultaneously. If no such elements exist, the iterators both point to the first element satisfying lower, or else are equal to end() if this latter element does not exist.
Complexity: O(log(n)).
Variants: In place of lower or upper (or both), the singular value boost::multi_index::unbounded can be provided. This acts as a predicate which all values of type key_type satisfy.

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 ordered indices with respect to serialization of their embedding containers, Use the concepts defined in the multi_index_container serialization section.

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

Requires: Additionally to the general requirements, value_comp() must be serialization-compatible with m.get<i>().value_comp(), where i is the position of the ordered index in the container.
Postconditions: On succesful 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()).

Requires: it is a valid iterator of the index. The associated multi_index_container has been previously saved.

Postconditions: On succesful 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.