#include <CGAL/Compact_container.h>

Definition

template<typename T, typename Allocator>
class CGAL::Compact_container< T, Allocator >

An object of the class Compact_container is a container of objects of type T.

This container matches all the standard requirements for reversible containers, except that the complexity of its iterator increment and decrement operations is not always guaranteed to be amortized constant time.

This container is not a standard sequence nor associative container, which means the elements are stored in no particular order, and it is not possible to specify a particular place in the iterator sequence where to insert new objects. However, all dereferenceable iterators are still valid after calls to insert() and erase(), except those that have been erased (it behaves similarly to std::list).

The main feature of this container is that it is very memory efficient: its memory size is N*sizeof(T)+o(N), where N is the maximum size that the container has had in its past history, its capacity() (the memory of erased elements is not deallocated until destruction of the container or a call to clear()). This container has been developed in order to store large graph-like data structures like the triangulation and the halfedge data structures.

It supports bidirectional iterators and allows a constant time amortized insert() operation. You cannot specify where to insert new objects (i.e. you don't know where they will end up in the iterator sequence, although insert() returns an iterator pointing to the newly inserted object). You can erase any element with a constant time complexity.

Summary of the differences with std::list: it is more compact in memory since it doesn't store two additional pointers for the iterator needs. It doesn't deallocate elements until the destruction or clear() of the container. The iterator does not have constant amortized time complexity for the increment and decrement operations in all cases, only when not too many elements have not been freed (i.e. when the size() is close to the capacity()). Iterating from begin() to end() takes \(O(capacity())\) time, not size(). In the case where the container has a small size() compared to its capacity(), we advise to "defragment the memory" by copying the container if the iterator performance is needed.

The iterators themselves can be used as T, they provide the necessary functions to be used by Compact_container_traits<T>. Moreover, they also provide a default constructor value which is not singular: it is copyable, comparable, and guaranteed to be unique under comparison (like nullptr for pointers). This makes them suitable for use in geometric graphs like handles to vertices in triangulations.

In addition, in a way inspired from the Boost.Intrusive containers, it is possible to construct iterators from references to values in containers using the iterator_to and s_iterator_to functions.

The objects stored in the Compact_container can optionally store an "erase counter". If it exists, i.e. if the object is a model of the ObjectWithEraseCounter concept, each time an object is erased from the container, the erase counter of the object will be incremented. For example, this erase counter can be exploited using the CC_safe_handle helper class, so that one can know if a handle is still pointing to the same element. Note that this is meaningful only because the CGAL::Compact_container doesn't deallocate elements until the destruction or clear() of the container.

Parameters

The parameter T is required to have a copy constructor and an assignment operator. It also needs to provide access to an internal pointer via Compact_container_traits<T>.

The equality test and the relational order require the operators == and < for T respectively.

The parameter Allocator has to match the standard allocator requirements, with value type T. This parameter has the default value CGAL_ALLOCATOR(T).

Related Functions
(Note that these are not member functions.)
template<class T , class A >
std::size_t	hash_value (const Compact_container< T, A >::iterator i)
	returns a hash value for the pointee of `i`.

Types
typedef unspecified_type	value_type

typedef unspecified_type	reference

typedef unspecified_type	const_reference

typedef unspecified_type	pointer

typedef unspecified_type	const_pointer

typedef unspecified_type	size_type

typedef unspecified_type	difference_type

typedef unspecified_type	iterator

typedef unspecified_type	const_iterator

typedef unspecified_type	reverse_iterator

typedef unspecified_type	const_reverse_iterator

typedef unspecified_type	allocator_type

Creation
	Compact_container (const Allocator &a=Allocator())
	introduces an empty container `cc`, eventually specifying a particular allocator `a` as well.

template<class InputIterator >
	Compact_container (InputIterator first, InputIterator last, const Allocator &a=Allocator())
	a container with copies from the range [`first,last`), eventually specifying a particular allocator.

	Compact_container (const Compact_container< T, Allocator > &cc2)
	copy constructor.

Compact_container< T, Allocator > &	operator= (const Compact_container< T, Allocator > &cc2)
	assignment.

void	swap (Compact_container< T, Allocator > &cc2)
	swaps the contents of `cc` and `cc2` in constant time complexity.

void	reserve (size_type value)
	if `value` is less than or equal to `capacity()`, this call has no effect.

Access Member Functions
iterator	begin ()
	returns a mutable iterator referring to the first element in `cc`.

const_iterator	begin () const
	returns a constant iterator referring to the first element in `cc`.

iterator	end ()
	returns a mutable iterator which is the past-end-value of `cc`.

const_iterator	end () const
	returns a constant iterator which is the past-end-value of `cc`.

reverse_iterator	rbegin ()

const_reverse_iterator	rbegin () const

reverse_iterator	rend ()

const_reverse_iterator	rend () const

iterator	iterator_to (reference value) const
	returns an iterator which points to `value`.

const_iterator	iterator_to (const_reference value) const
	returns an iterator which points to `value`.

bool	empty () const
	returns `true` iff `cc` is empty.

size_type	size () const
	returns the number of items in `cc`.

size_type	max_size () const
	returns the maximum possible size of the container `cc`.

size_type	capacity () const
	returns the total number of elements that `cc` can hold without requiring reallocation.

bool	is_used (const_iterator pos) const
	returns true if the element `pos` is used (i.e. valid).

bool	is_used (size_type i) const
	returns true if the element at position `i` in the container is used (i.e. valid).

const T &	operator[] (size_type i) const
	returns the element at pos `i` in the container.

T &	operator[] (size_type i)
	returns the element at pos `i` in the container.

Allocator	get_allocator () const
	returns the allocator.

static iterator	s_iterator_to (reference value)
	returns an iterator which points to `value`;

static const_iterator	s_iterator_to (const_reference value)
	returns an iterator which points to `value`;

Insertion
iterator	insert (const T &t)
	inserts a copy of `t` in `cc` and returns the iterator pointing to it.

template<class InputIterator >
void	insert (InputIterator first, InputIterator last)
	inserts the range [`first, last`) in `cc`.

template<class InputIterator >
void	assign (InputIterator first, InputIterator last)
	erases all the elements of `cc`, then inserts the range [`first, last`) in `cc`.

template<class T1 >
iterator	emplace (const T1 &t1)
	constructs an object of type `T` with the constructor that takes `t1` as argument, inserts it in `cc`, and returns the iterator pointing to it.

Removal
void	erase (iterator pos)
	removes the item pointed by `pos` from `cc`.

void	erase (iterator first, iterator last)
	removes the items from the range [`first, last`) from `cc`.

void	clear ()
	all items in `cc` are deleted, and the memory is deallocated.

Ownership testing
The following functions are mostly helpful for efficient debugging, since their complexity is \(O(\sqrt{\mathrm{c.capacity()}})\).
bool	owns (const_iterator pos)
	returns whether `pos` is in the range `[cc.begin(), cc.end()]` (`cc.end()` included).

bool	owns_dereferenceable (const_iterator pos)
	returns whether `pos` is in the range `[cc.begin(), cc.end())` (`cc.end()` excluded).

Merging
void	merge (Compact_container< T, Allocator > &cc)
	adds the items of `cc2` to the end of `cc` and `cc2` becomes empty.

Comparison Operations
bool	operator== (const Compact_container< T, Allocator > &cc) const
	test for equality: Two containers are equal, iff they have the same size and if their corresponding elements are equal.

bool	operator!= (const Compact_container< T, Allocator > &cc) const
	test for inequality: returns `!(c == cc)`.

bool	operator< (const Compact_container< T, Allocator > &cc2) const
	compares in lexicographical order.

bool	operator> (const Compact_container< T, Allocator > &cc2) const
	returns `cc2 <cc`.

bool	operator<= (const Compact_container< T, Allocator > &cc2) const
	returns `!(cc > cc2)`.

bool	operator>= (const Compact_container< T, Allocator > &cc2) const
	returns `!(cc < cc2)`.