CGAL::Unique_hash_map< Key, Data, UniqueHashFunction, Allocator > Class Template Reference

#include <CGAL/Unique_hash_map.h>

Definition

An instance of the class template Unique_hash_map is an injective mapping from the set of keys of type Key to the set of variables of type Data.

New keys can be inserted at any time, however keys cannot be individually deleted.

An object hash of the type UniqueHashFunction returns a unique integer index hash(key) of type std::size_t for all objects \( key\) stored in map. The template parameter has as default the Handle_hash_function that hashes all types of pointers, handles, iterators, and circulators.

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

All variables are initialized to default_data, a value of type Data specified in the definition of map.

See also

UniqueHashFunction

CGAL::Handle_hash_function

Implementation

Unique_hash_map is implemented via a chained hashing scheme. Access operations map[i] take expected time \( O(1)\). The table_size parameter passed to chained hashing can be used to avoid unnecessary rehashing when set to the number of expected elements in the map. The design is derived from the STL hash_map and the LEDA type map. Its specialization on insertion only and unique hash values allow for a more time- and space-efficient implementation, see also [2], Chapter 5. This implementation makes also use of sentinels that lead to defined keys that have not been inserted.

Types
In compliance with stl, the types key_type, data_type, and hasher are defined as well.
typedef unspecified_type	Key
	the Key type.
typedef unspecified_type	Data
	the Data type.
typedef unspecified_type	Hash_function
	the unique hash function type.

Creation
	Unique_hash_map (const Data &default=Data(), std::size_t table_size=1, const Hash_function &fct=Hash_function())
	creates an injective function from Key to the set of unused variables of type Data, sets default_data to default, passes the table_size as argument to the internal implementation, and initializes the hash function with fct.
	Unique_hash_map (Key first1, Key beyond1, Data first2, const Data &default=Data(), std::size_t table_size=1, const Hash_function &fct=Hash_function())
	creates an injective function from Key to the set of unused variables of type Data, sets default_data to default, passes the table_size as argument to the internal implementation, initializes the hash function with fct, and inserts all keys from the range [first1,beyond1). More...

Operations
Data	default_value () const
	the current default_value.
Hash_function	hash_function () const
	the current hash function.
bool	is_defined (const Key &key) const
	returns true if \( key\) is defined in *this. More...
void	clear ()
	resets *this to the injective function from Key to the set of unused variables of type Data. More...
void	clear (const Data &default)
	resets *this to the injective function from Key to the set of unused variables of type Data and sets default_data to default.
Data &	operator[] (const Key &key)
	returns a reference to the variable map(key). More...
const Data &	operator[] (const Key &key) const
	returns a const reference to the variable *this(key). More...
Data	insert (Key first1, Key beyond1, Data first2)
	inserts all keys from the range [first1,beyond1). More...

Constructor & Destructor Documentation

Unique_hash_map()

template<typename Key , typename Data , typename UniqueHashFunction , typename Allocator >

CGAL::Unique_hash_map< Key, Data, UniqueHashFunction, Allocator >::Unique_hash_map	(	Key	first1,
		Key	beyond1,
		Data	first2,
		const Data &	default = Data(),
		std::size_t	table_size = 1,
		const Hash_function &	fct = Hash_function()
	)

creates an injective function from Key to the set of unused variables of type Data, sets default_data to default, passes the table_size as argument to the internal implementation, initializes the hash function with fct, and inserts all keys from the range [first1,beyond1).

The data variable for each inserted key is initialized with the corresponding value from the range [first2, first2 + (beyond1-first1)).

Precondition

The increment operator must be defined for values of type Key and for values of type Data. beyond1 must be reachable from first1 using increments.

Member Function Documentation

clear()

template<typename Key , typename Data , typename UniqueHashFunction , typename Allocator >

void CGAL::Unique_hash_map< Key, Data, UniqueHashFunction, Allocator >::clear

(

)

resets *this to the injective function from Key to the set of unused variables of type Data.

The default_data remains unchanged.

insert()

template<typename Key , typename Data , typename UniqueHashFunction , typename Allocator >

Data CGAL::Unique_hash_map< Key, Data, UniqueHashFunction, Allocator >::insert	(	Key	first1,
		Key	beyond1,
		Data	first2
	)

inserts all keys from the range [first1,beyond1).

The data variable for each inserted key is initilized with the corresponding value from the range [first2, first2 + (beyond1-first1)). Returns first2 + (beyond1-first1).

Precondition

The increment operator must be defined for values of type Key and for values of type Data. beyond1 must be reachable from first1 using increments.

is_defined()

template<typename Key , typename Data , typename UniqueHashFunction , typename Allocator >

bool CGAL::Unique_hash_map< Key, Data, UniqueHashFunction, Allocator >::is_defined

(

const Key &

key

)

const

returns true if \( key\) is defined in *this.

Note that there can be keys defined that have not been inserted explicitly. Their variables are initialized to default_value.

operator[]() [1/2]

template<typename Key , typename Data , typename UniqueHashFunction , typename Allocator >

Data& CGAL::Unique_hash_map< Key, Data, UniqueHashFunction, Allocator >::operator[]

(

const Key &

key

)

returns a reference to the variable map(key).

If key has not been inserted into map before, key is inserted and initialized with default_value.

operator[]() [2/2]

template<typename Key , typename Data , typename UniqueHashFunction , typename Allocator >

const Data& CGAL::Unique_hash_map< Key, Data, UniqueHashFunction, Allocator >::operator[]

(

const Key &

key

)

const

returns a const reference to the variable *this(key).

If key has not been inserted into *this before, a const reference to the default_value is returned. However, key is not inserted into *this.