The QContiguousCache class is a template class that provides a contiguous cache.\reentrant. More...

#include <qcontiguouscache.h>

Public Types
typedef T	value_type

typedef value_type *	pointer

typedef const value_type *	const_pointer

typedef value_type &	reference

typedef const value_type &	const_reference

typedef qptrdiff	difference_type

typedef qsizetype	size_type

Public Member Functions
	QContiguousCache (qsizetype capacity=0)

	QContiguousCache (const QContiguousCache< T > &v)

	~QContiguousCache ()

void	detach ()

bool	isDetached () const

QContiguousCache< T > &	operator= (const QContiguousCache< T > &other)

void	swap (QContiguousCache &other) noexcept

template<typename U = T>
QTypeTraits::compare_eq_result< U >	operator== (const QContiguousCache< T > &other) const

template<typename U = T>
QTypeTraits::compare_eq_result< U >	operator!= (const QContiguousCache< T > &other) const

qsizetype	capacity () const

qsizetype	count () const

qsizetype	size () const

bool	isEmpty () const

bool	isFull () const

qsizetype	available () const

void	clear ()

void	setCapacity (qsizetype size)

const T &	at (qsizetype pos) const

T &	operator[] (qsizetype i)

const T &	operator[] (qsizetype i) const

void	append (T &&value)

void	append (const T &value)

void	prepend (T &&value)

void	prepend (const T &value)

void	insert (qsizetype pos, T &&value)

void	insert (qsizetype pos, const T &value)

bool	containsIndex (qsizetype pos) const

qsizetype	firstIndex () const

qsizetype	lastIndex () const

const T &	first () const

const T &	last () const

T &	first ()

T &	last ()

void	removeFirst ()

T	takeFirst ()

void	removeLast ()

T	takeLast ()

bool	areIndexesValid () const

void	normalizeIndexes ()

Detailed Description

template<typename T>
class QContiguousCache< T >

The QContiguousCache class is a template class that provides a contiguous cache.

\reentrant.

\inmodule QtCore

Since: 4.6

The QContiguousCache class provides an efficient way of caching items for display in a user interface view. Unlike QCache, it adds a restriction that elements within the cache are contiguous. This has the advantage of matching how user interface views most commonly request data, as a set of rows localized around the current scrolled position. This restriction allows the cache to consume less memory and processor cycles than QCache.

QContiguousCache operates on a fixed capacity, set with setCapacity() or passed as a parameter to the constructor. This capacity is the upper bound on memory usage by the cache itself, not including the memory allocated by the elements themselves. Note that a cache with a capacity of zero (the default) means no items will be stored: the insert(), append() and prepend() operations will effectively be no-ops. Therefore, it's important to set the capacity to a reasonable value before adding items to the cache.

The simplest way of using a contiguous cache is to use the append() and prepend().

If the cache is full then the item at the opposite end of the cache from where the new item is appended or prepended will be removed.

This usage can be further optimized by using the insert() function in the case where the requested row is a long way from the currently cached items. If there is a gap between where the new item is inserted and the currently cached items then the existing cached items are first removed to retain the contiguous nature of the cache. Hence it is important to take some care then when using insert() in order to avoid unwanted clearing of the cache.

The range of valid indexes for the QContiguousCache class are from 0 to INT_MAX. Calling prepend() such that the first index would become less than 0 or append() such that the last index would become greater than INT_MAX can result in the indexes of the cache being invalid. When the cache indexes are invalid it is important to call normalizeIndexes() before calling any of containsIndex(), firstIndex(), lastIndex(), at() or \l{QContiguousCache::operator[]()}{operator[]()}. Calling these functions when the cache has invalid indexes will result in undefined behavior. The indexes can be checked by using areIndexesValid()

In most cases the indexes will not exceed 0 to INT_MAX, and normalizeIndexes() will not need to be used.

See the \l{Contiguous Cache Example}{Contiguous Cache} example.

Definition at line 75 of file qcontiguouscache.h.

Member Typedef Documentation

◆ const_pointer

template<typename T >

QContiguousCache< T >::const_pointer

Definition at line 84 of file qcontiguouscache.h.

◆ const_reference

template<typename T >

QContiguousCache< T >::const_reference

Definition at line 86 of file qcontiguouscache.h.

◆ difference_type

template<typename T >

QContiguousCache< T >::difference_type

Definition at line 87 of file qcontiguouscache.h.

◆ pointer

template<typename T >

QContiguousCache< T >::pointer

Definition at line 83 of file qcontiguouscache.h.

◆ reference

template<typename T >

QContiguousCache< T >::reference

Definition at line 85 of file qcontiguouscache.h.

◆ size_type

template<typename T >

QContiguousCache< T >::size_type

Definition at line 88 of file qcontiguouscache.h.

◆ value_type

template<typename T >

QContiguousCache< T >::value_type

Definition at line 82 of file qcontiguouscache.h.

Constructor & Destructor Documentation

◆ QContiguousCache() [1/2]

template<typename T >

QContiguousCache< T >::QContiguousCache ( qsizetype capacity = 0 )

explicit

Constructs a cache with the given capacity.

See also: setCapacity()

Definition at line 278 of file qcontiguouscache.h.

◆ QContiguousCache() [2/2]

template<typename T >

template< typename T > QContiguousCache< T >::QContiguousCache ( const QContiguousCache< T > & other )

inline

Constructs a copy of other.

This operation takes \l{constant time}, because QContiguousCache is \l{implicitly shared}. This makes returning a QContiguousCache from a function very fast. If a shared instance is modified, it will be copied (copy-on-write), and that takes \l{linear time}.

See also: operator=()

Definition at line 91 of file qcontiguouscache.h.

◆ ~QContiguousCache()

template<typename T >

template< typename T > QContiguousCache< T >::~QContiguousCache ( )

inline

Destroys the cache.

Definition at line 93 of file qcontiguouscache.h.

Member Function Documentation

◆ append() [1/2]

template<typename T >

void QContiguousCache< T >::append ( const T & value )

Inserts value at the end of the cache. If the cache is already full the item at the start of the cache will be removed.

See also: prepend(), insert(), isFull()

Definition at line 333 of file qcontiguouscache.h.

◆ append() [2/2]

template<typename T >

void QContiguousCache< T >::append ( T && value )

Definition at line 314 of file qcontiguouscache.h.

◆ areIndexesValid()

template<typename T >

template< typename T > bool QContiguousCache< T >::areIndexesValid ( ) const

inline

Returns whether the indexes for items stored in the cache are valid. Indexes can become invalid if items are appended after the index position INT_MAX or prepended before the index position 0. This is only expected to occur in very long lived circular buffer style usage of the contiguous cache. Indexes can be made valid again by calling normalizeIndexes().

See also: normalizeIndexes(), append(), prepend()

Definition at line 164 of file qcontiguouscache.h.

◆ at()

template<typename T >

const T & QContiguousCache< T >::at ( qsizetype i ) const

inline

Returns the item at index position i in the cache. i must be a valid index position in the cache (i.e, firstIndex() <= i <= lastIndex()).

The indexes in the cache refer to the number of positions the item is from the first item appended into the cache. That is to say a cache with a capacity of 100, that has had 150 items appended will have a valid index range of 50 to 149. This allows inserting and retrieving items into the cache based on a theoretical infinite list

See also: firstIndex(), lastIndex(), insert(), operator[]()

Definition at line 420 of file qcontiguouscache.h.

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◆ available()

template<typename T >

template< typename T > qsizetype QContiguousCache< T >::available ( ) const

inline

Returns the number of items that can be added to the cache before it becomes full.

See also: size(), capacity(), isFull()

Definition at line 132 of file qcontiguouscache.h.

◆ capacity()

template<typename T >

template< typename T > qsizetype QContiguousCache< T >::capacity ( ) const

inline

Returns the number of items the cache can store before it is full. When a cache contains a number of items equal to its capacity, adding new items will cause items farthest from the added item to be removed.

See also: setCapacity(), size()

Definition at line 126 of file qcontiguouscache.h.

◆ clear()

template<typename T >

void QContiguousCache< T >::clear

Removes all items from the cache. The capacity is unchanged.

Definition at line 245 of file qcontiguouscache.h.

◆ containsIndex()

template<typename T >

template< typename T > bool QContiguousCache< T >::containsIndex ( qsizetype i ) const

inline

Returns true if the cache's index range includes the given index i.

See also: firstIndex(), lastIndex()

Definition at line 149 of file qcontiguouscache.h.

◆ count()

template<typename T >

template< typename T > qsizetype QContiguousCache< T >::count ( ) const

inline

Same as size().

Definition at line 127 of file qcontiguouscache.h.

◆ detach()

template<typename T >

template< typename T > void QContiguousCache< T >::detach ( )

inline

Definition at line 95 of file qcontiguouscache.h.

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◆ first() [1/2]

template<typename T >

template< typename T > T & QContiguousCache< T >::first ( )

inline

Returns a reference to the first item in the cache. This function assumes that the cache isn't empty.

See also: last(), isEmpty()

Definition at line 155 of file qcontiguouscache.h.

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◆ first() [2/2]

template<typename T >

template< typename T > const T & QContiguousCache< T >::first ( ) const

inline

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Definition at line 153 of file qcontiguouscache.h.

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◆ firstIndex()

template<typename T >

template< typename T > qsizetype QContiguousCache< T >::firstIndex ( ) const

inline

Returns the first valid index in the cache. The index will be invalid if the cache is empty.

See also: capacity(), size(), lastIndex()

Definition at line 150 of file qcontiguouscache.h.

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◆ insert() [1/2]

template<typename T >

void QContiguousCache< T >::insert	(	qsizetype	i,
		const T &	value
	)

Inserts the value at the index position i. If the cache already contains an item at i then that value is replaced. If i is either one more than lastIndex() or one less than firstIndex() it is the equivalent to an append() or a prepend().

If the given index i is not within the current range of the cache nor adjacent to the bounds of the cache's index range, the cache is first cleared before inserting the item. At this point the cache will have a size of 1. It is worthwhile taking effort to insert items in an order that starts adjacent to the current index range for the cache.

The range of valid indexes for the QContiguousCache class are from 0 to INT_MAX. Inserting outside of this range has undefined behavior.

See also: prepend(), append(), isFull(), firstIndex(), lastIndex()

Definition at line 415 of file qcontiguouscache.h.

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◆ insert() [2/2]

template<typename T >

void QContiguousCache< T >::insert	(	qsizetype	pos,
		T &&	value
	)

Definition at line 392 of file qcontiguouscache.h.

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◆ isDetached()

template<typename T >

template< typename T > bool QContiguousCache< T >::isDetached ( ) const

inline

Definition at line 96 of file qcontiguouscache.h.

◆ isEmpty()

template<typename T >

template< typename T > bool QContiguousCache< T >::isEmpty ( ) const

inline

Returns true if no items are stored within the cache.

See also: size(), capacity()

Definition at line 130 of file qcontiguouscache.h.

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◆ isFull()

template<typename T >

template< typename T > bool QContiguousCache< T >::isFull ( ) const

inline

Returns true if the number of items stored within the cache is equal to the capacity of the cache.

See also: size(), capacity()

Definition at line 131 of file qcontiguouscache.h.

◆ last() [1/2]

template<typename T >

template< typename T > T & QContiguousCache< T >::last ( )

inline

Returns a reference to the last item in the cache. This function assumes that the cache isn't empty.

See also: first(), isEmpty()

Definition at line 156 of file qcontiguouscache.h.

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◆ last() [2/2]

template<typename T >

template< typename T > const T & QContiguousCache< T >::last ( ) const

inline

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Definition at line 154 of file qcontiguouscache.h.

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◆ lastIndex()

template<typename T >

template< typename T > qsizetype QContiguousCache< T >::lastIndex ( ) const

inline

Returns the last valid index in the cache. The index will be invalid if the cache is empty.

See also: capacity(), size(), firstIndex()

Definition at line 151 of file qcontiguouscache.h.

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◆ normalizeIndexes()

template<typename T >

template< typename T > void QContiguousCache< T >::normalizeIndexes ( )

inline

Moves the first index and last index of the cache such that they point to valid indexes. The function does not modify the contents of the cache or the ordering of elements within the cache.

It is provided so that index overflows can be corrected when using the cache as a circular buffer.

See also: areIndexesValid(), append(), prepend()

Definition at line 167 of file qcontiguouscache.h.

◆ operator!=()

template<typename T >

template<typename U = T>

template< typename T > bool QContiguousCache< T >::operator!= ( const QContiguousCache< T > & other ) const

inline

Returns true if other is not equal to this cache; otherwise returns false.

Two caches are considered equal if they contain the same values at the same indexes. This function requires the value type to implement the operator==().

See also: operator==()

Definition at line 119 of file qcontiguouscache.h.

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◆ operator=()

template<typename T >

QContiguousCache< T > & QContiguousCache< T >::operator= ( const QContiguousCache< T > & other )

Assigns other to this cache and returns a reference to this cache.

Move-assigns other to this QContiguousCache instance.

Since: 5.2

Definition at line 288 of file qcontiguouscache.h.

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◆ operator==()

template<typename T >

template<typename U = T>

template< typename T > bool QContiguousCache< T >::operator== ( const QContiguousCache< T > & other ) const

inline

Returns true if other is equal to this cache; otherwise returns false.

Two caches are considered equal if they contain the same values at the same indexes. This function requires the value type to implement the operator==().

See also: operator!=()

Definition at line 104 of file qcontiguouscache.h.

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◆ operator[]() [1/2]

template<typename T >

T & QContiguousCache< T >::operator[] ( qsizetype i )

inline

Returns the item at index position i as a modifiable reference. If the cache does not contain an item at the given index position i then it will first insert an empty item at that position.

In most cases it is better to use either at() or insert().

Note: This non-const overload of operator[] requires QContiguousCache to make a deep copy. Use at() for read-only access to a non-const QContiguousCache.

See also: insert(), at()

Definition at line 427 of file qcontiguouscache.h.

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◆ operator[]() [2/2]

template<typename T >

const T & QContiguousCache< T >::operator[] ( qsizetype i ) const

inline

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Same as at(i).

Definition at line 423 of file qcontiguouscache.h.

◆ prepend() [1/2]

template<typename T >

void QContiguousCache< T >::prepend ( const T & value )

Inserts value at the start of the cache. If the cache is already full the item at the end of the cache will be removed.

See also: append(), insert(), isFull()

Definition at line 372 of file qcontiguouscache.h.

◆ prepend() [2/2]

template<typename T >

void QContiguousCache< T >::prepend ( T && value )

Definition at line 352 of file qcontiguouscache.h.

◆ removeFirst()

template<typename T >

void QContiguousCache< T >::removeFirst

inline

Removes the first item from the cache. This function assumes that the cache isn't empty.

See also: removeLast()

Definition at line 436 of file qcontiguouscache.h.

◆ removeLast()

template<typename T >

void QContiguousCache< T >::removeLast

inline

Removes the last item from the cache. This function assumes that the cache isn't empty.

See also: removeFirst()

Definition at line 448 of file qcontiguouscache.h.

◆ setCapacity()

template<typename T >

void QContiguousCache< T >::setCapacity ( qsizetype size )

Sets the capacity of the cache to the given size. A cache can hold a number of items equal to its capacity. When inserting, appending or prepending items to the cache, if the cache is already full then the item farthest from the added item will be removed.

If the given size is smaller than the current count of items in the cache then only the last size items from the cache will remain.

See also: capacity(), isFull()

Definition at line 208 of file qcontiguouscache.h.

◆ size()

template<typename T >

template< typename T > qsizetype QContiguousCache< T >::size ( ) const

inline

Returns the number of items contained within the cache.

See also: capacity()

Definition at line 128 of file qcontiguouscache.h.

◆ swap()

template<typename T >

template< typename T > void QContiguousCache< T >::swap ( QContiguousCache< T > & other )

inlinenoexcept

Since: 4.8

Swaps cache other with this cache. This operation is very fast and never fails.

Definition at line 100 of file qcontiguouscache.h.

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◆ takeFirst()

template<typename T >

T QContiguousCache< T >::takeFirst

inline

Removes the first item in the cache and returns it. This function assumes that the cache isn't empty.

If you don't use the return value, removeFirst() is more efficient.

See also: takeLast(), removeFirst()

Definition at line 458 of file qcontiguouscache.h.

◆ takeLast()

template<typename T >

T QContiguousCache< T >::takeLast

inline

Removes the last item in the cache and returns it. This function assumes that the cache isn't empty.

If you don't use the return value, removeLast() is more efficient.

See also: takeFirst(), removeLast()

Definition at line 462 of file qcontiguouscache.h.

The documentation for this class was generated from the following files:

src/corelib/tools/qcontiguouscache.h
src/corelib/tools/qcontiguouscache.cpp

Public Types

Public Member Functions

Detailed Description

template<typename T> class QContiguousCache< T >

Member Typedef Documentation

◆ const_pointer

◆ const_reference

◆ difference_type

◆ pointer

◆ reference

◆ size_type

◆ value_type

Constructor & Destructor Documentation

◆ QContiguousCache() [1/2]

◆ QContiguousCache() [2/2]

◆ ~QContiguousCache()

Member Function Documentation

◆ append() [1/2]

◆ append() [2/2]

◆ areIndexesValid()

◆ at()

◆ available()

◆ capacity()

◆ clear()

◆ containsIndex()

◆ count()

◆ detach()

◆ first() [1/2]

◆ first() [2/2]

◆ firstIndex()

◆ insert() [1/2]

◆ insert() [2/2]

◆ isDetached()

◆ isEmpty()

◆ isFull()

◆ last() [1/2]

◆ last() [2/2]

◆ lastIndex()

◆ normalizeIndexes()

◆ operator!=()

◆ operator=()

◆ operator==()

◆ operator[]() [1/2]

◆ operator[]() [2/2]

◆ prepend() [1/2]

◆ prepend() [2/2]

◆ removeFirst()

◆ removeLast()

◆ setCapacity()

◆ size()

◆ swap()

◆ takeFirst()

◆ takeLast()

template<typename T>
class QContiguousCache< T >