RWHashTable Class Reference

A simple hash table for objects inheriting from RWCollectable. Uses chaining (as implemented by class RWSlistCollectables) to resolve hash collisions. More...

#include <rw/hashtab.h>

Inheritance diagram for RWHashTable:

Public Member Functions
	RWHashTable ()
	RWHashTable (size_t N)
	RWHashTable (const RWHashTable &t)
	RWHashTable (RWHashTable &&t)
virtual void	apply (RWapplyCollectable ap, void *)
virtual void	clear ()
virtual RWCollectable *	copy () const
virtual size_t	entries () const
virtual RWCollectable *	find (const RWCollectable *) const
virtual RWCollectable *	insert (RWCollectable *a)
virtual RWClassID	isA () const
virtual bool	isEmpty () const
virtual bool	isEqual (const RWCollectable *) const
virtual RWConstIterator *	newConstIterator () const
virtual RWIterator *	newIterator ()
virtual RWCollectable *	newSpecies () const
virtual size_t	occurrencesOf (const RWCollectable *) const
bool	operator!= (const RWHashTable &) const
bool	operator<= (const RWHashTable &t) const
RWHashTable &	operator= (const RWHashTable &t)
RWHashTable &	operator= (RWHashTable &&t)
bool	operator== (const RWHashTable &t) const
virtual RWCollectable *	remove (const RWCollectable *)
virtual void	resize (size_t n=0)
void	swap (RWHashTable &t)
Public Member Functions inherited from RWCollection
virtual	~RWCollection ()
RWBag	asBag () const
RWBinaryTree	asBinaryTree () const
RWOrdered	asOrderedCollection () const
RWSet	asSet () const
RWBinaryTree	asSortedCollection () const
virtual RWspace	binaryStoreSize () const
virtual void	clearAndDestroy ()
virtual bool	contains (const RWCollectable *target) const
void	operator+= (const RWCollection &c)
void	operator-= (const RWCollection &c)
virtual void	removeAndDestroy (const RWCollectable *target)
virtual void	restoreGuts (RWvistream &)
virtual void	restoreGuts (RWFile &)
virtual void	saveGuts (RWvostream &) const
virtual void	saveGuts (RWFile &) const
RWCollection *	select (RWtestCollectable tst, void *vp) const
Public Member Functions inherited from RWCollectable
virtual	~RWCollectable ()
virtual int	compareTo (const RWCollectable *) const
virtual unsigned	hash () const
RWspace	recursiveStoreSize () const
RWStringID	stringID () const

Additional Inherited Members
Static Public Member Functions inherited from RWCollectable
static RWClassID	classID (const RWStringID &name)
static RWClassID	classIsA ()
static bool	isAtom (RWClassID id)
static RWspace	nilStoreSize ()
Static Public Attributes inherited from RWCollection
static size_t	DEFAULT_CAPACITY
Related Functions inherited from RWCollection
typedef void(*	RWapplyCollectable) (RWCollectable *, void *)
typedef bool(*	RWtestCollectable) (const RWCollectable *, const void *)
typedef bool(*	RWtestCollectablePair) (const RWCollectable *, const RWCollectable *, const void *)

Detailed Description

This class is a simple hash table for objects inheriting from RWCollectable. It uses chaining (as implemented by class RWSlistCollectables) to resolve hash collisions. Duplicate objects are allowed. An object stored by RWHashTable must inherit from the abstract base class RWCollectable, with suitable definition for virtual functions hash() and isEqual().

To find an object that matches a key, the key's virtual function hash() is first called to determine in which bucket the object occurs. The bucket is then searched linearly by calling the virtual function isEqual() for each candidate, with the key as the argument. The first object to return true is the returned object.

The initial number of buckets in the table is set by the constructor. There is a default value. If the number of items in the collection greatly exceeds the number of buckets then efficiency sags because each bucket must be searched linearly. The number of buckets can be changed by calling member function resize(). This requires that all objects be rehashed.

The iterator for this class is RWHashTableIterator.

Synopsis

#include <rw/hashtab.h>
RWHashTable h ;

Persistence

Polymorphic

Example

#include <rw/hashtab.h>
#include <rw/tools/ctdatetime.h>

int main ()
{
    RWHashTable table;

    RWCollectableDateTime *july = new RWCollectableDateTime ("July 7, 1990", RWDateTime::setDate);
    RWCollectableDateTime *may  = new RWCollectableDateTime ("May 1, 1977", RWDateTime::setDate);
    RWCollectableDateTime *feb  = new RWCollectableDateTime ("Feb 22, 1983", RWDateTime::setDate);
    RWCollectableDateTime *aug  = new RWCollectableDateTime ("Aug 2, 1966", RWDateTime::setDate);

    table.insert(july);
    table.insert(may);
    table.insert(feb);
    table.insert(aug);

    std::cout << "Table contains " << table.entries() << " entries ";

    RWCollectableDateTime key("Feb 22, 1983", RWDateTime::setDate);
    std::cout << "and it does"
              << (table.contains(&key) ? " " : " not ")
              << "contain the key " << key << std::endl;

    delete july;
    delete may;
    delete feb;
    delete aug;

    return 0;
}

Program output:

Table contains 4 entries and it does contain the key Tue Feb 22 00:00:00 1983

Constructor & Destructor Documentation

RWHashTable::RWHashTable

(

)

Constructs an empty hash table with RWCollection::DEFAULT_CAPACITY buckets.

RWHashTable::RWHashTable

(

size_t

N

)

Constructs an empty hash table with N buckets.

RWHashTable::RWHashTable

(

const RWHashTable &

t

)

Copy constructor. Creates a new hash table as a shallow copy of the table t. The new table has the same number of buckets as the old table. Hence, the members need not be and will not be rehashed.

RWHashTable::RWHashTable

(

RWHashTable &&

t

)

Move constructor. The constructed RWHashTable takes ownership of the data owned by t.

Condition:

This method is available only on platforms with rvalue reference support.

Member Function Documentation

virtual void RWHashTable::apply ( RWapplyCollectable  ap, void *    )

virtual

Invokes the function pointer ap on each item in the collection in no particular order, due to the nature of hashing collections. The function pointed to by ap should take no action that could change the hash value or equality properties of the objects.

Implements RWCollection.

virtual void RWHashTable::clear ( )

virtual

Removes all objects from the collection. Does not delete the objects themselves.

Implements RWCollection.

Reimplemented in RWHashDictionary.

virtual RWCollectable* RWHashTable::copy ( ) const

virtual

Returns a new, copy-constructed object of the same type as self. The caller is responsible for deleting the object.

Reimplemented from RWCollectable.

Reimplemented in RWSet, RWIdentitySet, RWIdentityDictionary, and RWHashDictionary.

virtual size_t RWHashTable::entries ( ) const

inlinevirtual

Returns the total number of items in the collection.

Implements RWCollection.

virtual RWCollectable* RWHashTable::find ( const RWCollectable *  target ) const

virtual

Returns a pointer to the first item in the collection which "matches" the object pointed to by target or rwnil if no item was found. For most collections, an item "matches" the target if either isEqual() or compareTo() find equivalence, whichever is appropriate for the actual collection type. However, the "identity collections" (i.e., RWIdentitySet and RWIdentityDictionary) look for an item with the same address (i.e., "is identical to").

Implements RWCollection.

Reimplemented in RWHashDictionary, and RWIdentitySet.

virtual RWCollectable* RWHashTable::insert ( RWCollectable *  a )

virtual

Returns a if successful, otherwise rwnil.

Note

If self is a collection of key-value pairs (e.g. RWHashDictionary), this function throws std::bad_cast if c does not inherit from RWCollectableAssociation. If the collection does not contain an association with a key that "matches" the key of c, then a copy of the association is inserted and that association's key is returned. Otherwise, the insert fails by returning either rwnil or a pointer to the existing association's key.

Implements RWCollection.

Reimplemented in RWHashDictionary, RWSet, and RWIdentitySet.

virtual RWClassID RWHashTable::isA ( ) const

virtual

Returns __RWHASHTABLE.

Reimplemented from RWCollection.

Reimplemented in RWSet, RWIdentitySet, RWIdentityDictionary, and RWHashDictionary.

virtual bool RWHashTable::isEmpty ( ) const

inlinevirtual

Returns true if the collection is empty, otherwise returns false.

Implements RWCollection.

virtual bool RWHashTable::isEqual ( const RWCollectable *  t ) const

virtual

Behaves as if compareTo(t) was invoked, returning true if the result equals 0, false otherwise.

Reimplemented from RWCollectable.

Reimplemented in RWHashDictionary, RWSet, RWIdentityDictionary, and RWIdentitySet.

virtual RWConstIterator* RWHashTable::newConstIterator ( ) const

virtual

Returns a const pointer to a dynamically allocated iterator for the collection.

Implements RWCollection.

Reimplemented in RWHashDictionary, and RWSet.

virtual RWIterator* RWHashTable::newIterator ( )

virtual

Returns a dynamically allocated iterator for the collection.

Implements RWCollection.

Reimplemented in RWHashDictionary, and RWSet.

virtual RWCollectable* RWHashTable::newSpecies ( ) const

virtual

Returns a new, default-constructed object of the same type as self. The caller is responsible for deleting the object.

Reimplemented from RWCollectable.

Reimplemented in RWSet, RWIdentitySet, RWIdentityDictionary, and RWHashDictionary.

virtual size_t RWHashTable::occurrencesOf ( const RWCollectable *  t ) const

virtual

Returns the number of items in the collection which are "matches" for t. See function find() for a definition of matches.

Implements RWCollection.

Reimplemented in RWSet.

bool RWHashTable::operator!=

(

const RWHashTable &

)

const

Returns the negation of operator==().

bool RWHashTable::operator<=

(

const RWHashTable &

t

)

const

Returns true if self is a subset of t, that is, every element of self has a counterpart in t which isEqual().

RWHashTable& RWHashTable::operator=

(

const RWHashTable &

t

)

Assignment operator. Sets self as a shallow copy of t. Afterwards, the two tables have the same number of buckets. Hence, the members need not be and will not be rehashed.

RWHashTable& RWHashTable::operator=

(

RWHashTable &&

t

)

Move assignment. Self takes ownership of the data owned by t.

Condition:

This method is available only on platforms with rvalue reference support.

bool RWHashTable::operator==

(

const RWHashTable &

t

)

const

Returns true if self and t have the same number of elements and if for every key in self there is a corresponding key in t which isEqual().

virtual RWCollectable* RWHashTable::remove ( const RWCollectable *  target )

virtual

Removes and returns a pointer to the first item in the collection which "matches" the object pointed to by target. Returns nil if no object was found. Does not delete the object. See function find() for a definition of matches.

Implements RWCollection.

Reimplemented in RWHashDictionary, and RWIdentitySet.

virtual void RWHashTable::resize ( size_t  n = 0 )

virtual

Resizes the internal hash table to have n buckets. This causes rehashing all the members of the collection. If n is zero, resizes to 3*entries()/2.

void RWHashTable::swap

(

RWHashTable &

t

)

Swaps the data owned by self with the data owned by t.