\inmodule QtCore More...

#include <qcontiguouscache.h>

Collaboration diagram for QContiguousCache< T >:

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)
	Constructs a cache with the given capacity.

	QContiguousCache (const QContiguousCache< T > &v)
	Constructs a copy of other.

	~QContiguousCache ()
	Destroys the cache.

void	detach ()

bool	isDetached () const

QContiguousCache< T > &	operator= (const QContiguousCache< T > &other)
	Assigns other to this cache and returns a reference to this cache.

void	swap (QContiguousCache &other) noexcept

template<typename U = T>
QTypeTraits::compare_eq_result< U >	operator== (const QContiguousCache< T > &other) const
	Returns `true` if other is equal to this cache; otherwise returns `false`.

template<typename U = T>
QTypeTraits::compare_eq_result< U >	operator!= (const QContiguousCache< T > &other) const
	Returns `true` if other is not equal to this cache; otherwise returns `false`.

qsizetype	capacity () const
	Returns the number of items the cache can store before it is full.

qsizetype	count () const
	Same as size().

qsizetype	size () const
	Returns the number of items contained within the cache.

bool	isEmpty () const
	Returns `true` if no items are stored within the cache.

bool	isFull () const
	Returns `true` if the number of items stored within the cache is equal to the capacity of the cache.

qsizetype	available () const
	Returns the number of items that can be added to the cache before it becomes full.

void	clear ()
	Removes all items from the cache.

void	setCapacity (qsizetype size)
	Sets the capacity of the cache to the given size.

const T &	at (qsizetype pos) const
	Returns the item at index position i in the cache.

T &	operator[] (qsizetype i)
	Returns the item at index position i as a modifiable reference.

const T &	operator[] (qsizetype i) const
	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).

void	append (T &&value)

void	append (const T &value)
	Inserts value at the end of the cache.

void	prepend (T &&value)

void	prepend (const T &value)
	Inserts value at the start of the cache.

void	insert (qsizetype pos, T &&value)

void	insert (qsizetype pos, const T &value)
	Inserts the value at the index position i.

bool	containsIndex (qsizetype pos) const
	Returns `true` if the cache's index range includes the given index i.

qsizetype	firstIndex () const
	Returns the first valid index in the cache.

qsizetype	lastIndex () const
	Returns the last valid index in the cache.

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

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

T &	first ()
	Returns a reference to the first item in the cache.

T &	last ()
	Returns a reference to the last item in the cache.

void	removeFirst ()
	Removes the first item from the cache.

T	takeFirst ()
	Removes the first item in the cache and returns it.

void	removeLast ()
	Removes the last item from the cache.

T	takeLast ()
	Removes the last item in the cache and returns it.

bool	areIndexesValid () const
	Returns whether the indexes for items stored in the cache are valid.

void	normalizeIndexes ()
	Moves the first index and last index of the cache such that they point to valid indexes.

Detailed Description

template<typename T>
class QContiguousCache< T >

\inmodule QtCore

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

\reentrant

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().

MyRecord record(int row) const
{
    Q_ASSERT(row >= 0 && row < count());
 
    while (row > cache.lastIndex())
        cache.append(slowFetchRecord(cache.lastIndex()+1));
    while (row < cache.firstIndex())
        cache.prepend(slowFetchRecord(cache.firstIndex()-1));
 
    return cache.at(row);
}

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 45 of file qcontiguouscache.h.

Member Typedef Documentation

◆ const_pointer

template<typename T >

QContiguousCache< T >::const_pointer

Definition at line 54 of file qcontiguouscache.h.

◆ const_reference

template<typename T >

QContiguousCache< T >::const_reference

Definition at line 56 of file qcontiguouscache.h.

◆ difference_type

template<typename T >

QContiguousCache< T >::difference_type

Definition at line 57 of file qcontiguouscache.h.

◆ pointer

template<typename T >

QContiguousCache< T >::pointer

Definition at line 53 of file qcontiguouscache.h.

◆ reference

template<typename T >

QContiguousCache< T >::reference

Definition at line 55 of file qcontiguouscache.h.

◆ size_type

template<typename T >

QContiguousCache< T >::size_type

Definition at line 58 of file qcontiguouscache.h.

◆ value_type

template<typename T >

QContiguousCache< T >::value_type

Definition at line 52 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 248 of file qcontiguouscache.h.

References allocateData(), d, and Q_ASSERT.

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◆ 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 61 of file qcontiguouscache.h.

References d.

◆ ~QContiguousCache()

template<typename T >

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

inline

Destroys the cache.

Definition at line 63 of file qcontiguouscache.h.

References d.

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 303 of file qcontiguouscache.h.

References d.

◆ append() [2/2]

template<typename T >

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

Definition at line 284 of file qcontiguouscache.h.

References d.

◆ 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 134 of file qcontiguouscache.h.

References d.

◆ 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 390 of file qcontiguouscache.h.

References d, pos, and Q_ASSERT_X.

◆ 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 102 of file qcontiguouscache.h.

References d.

◆ 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 96 of file qcontiguouscache.h.

References d.

◆ clear()

template<typename T >

void QContiguousCache< T >::clear ( )

Removes all items from the cache.

The capacity is unchanged.

Definition at line 215 of file qcontiguouscache.h.

References allocateData(), d, and i.

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◆ 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 119 of file qcontiguouscache.h.

References d, and pos.

◆ count()

template<typename T >

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

inline

Same as size().

Definition at line 97 of file qcontiguouscache.h.

References d.

◆ detach()

template<typename T >

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

inline

Definition at line 65 of file qcontiguouscache.h.

References d.

Referenced by QContiguousCache< T >::first(), and QContiguousCache< T >::last().

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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 125 of file qcontiguouscache.h.

References d, QContiguousCache< T >::detach(), QContiguousCache< T >::isEmpty(), and Q_ASSERT.

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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 123 of file qcontiguouscache.h.

References d, QContiguousCache< T >::isEmpty(), and Q_ASSERT.

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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 120 of file qcontiguouscache.h.

References d.

Referenced by QContiguousCache< T >::operator==().

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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 385 of file qcontiguouscache.h.

References insert(), and pos.

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◆ insert() [2/2]

template<typename T >

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

Definition at line 362 of file qcontiguouscache.h.

References append(), clear(), d, pos, prepend(), and Q_ASSERT_X.

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◆ isDetached()

template<typename T >

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

inline

Definition at line 66 of file qcontiguouscache.h.

References d.

◆ 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 100 of file qcontiguouscache.h.

References d.

Referenced by QContiguousCache< T >::first(), QContiguousCache< T >::first(), QContiguousCache< T >::last(), and QContiguousCache< T >::last().

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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 101 of file qcontiguouscache.h.

References d.

◆ 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 126 of file qcontiguouscache.h.

References d, QContiguousCache< T >::detach(), QContiguousCache< T >::isEmpty(), and Q_ASSERT.

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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 124 of file qcontiguouscache.h.

References d, QContiguousCache< T >::isEmpty(), and Q_ASSERT.

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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 121 of file qcontiguouscache.h.

References d.

Referenced by QContiguousCache< T >::operator==().

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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.

QContiguousCache<int> cache(10);
cache.insert(INT_MAX, 1); // cache contains one value and has valid indexes, INT_MAX to INT_MAX
cache.append(2); // cache contains two values but does not have valid indexes.
cache.normalizeIndexes(); // cache has two values, 1 and 2.  New first index will be in the range of 0 to capacity().

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

Definition at line 137 of file qcontiguouscache.h.

References d.

◆ 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 89 of file qcontiguouscache.h.

References other().

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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 258 of file qcontiguouscache.h.

References d, and other().

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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 74 of file qcontiguouscache.h.

References at, d, QContiguousCache< T >::firstIndex(), i, QContiguousCache< T >::lastIndex(), and other().

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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 397 of file qcontiguouscache.h.

References d, insert(), and pos.

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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 393 of file qcontiguouscache.h.

References at, and pos.

◆ 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 342 of file qcontiguouscache.h.

References d.

◆ prepend() [2/2]

template<typename T >

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

Definition at line 322 of file qcontiguouscache.h.

References d.

◆ 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 406 of file qcontiguouscache.h.

References d, and Q_ASSERT.

◆ 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 418 of file qcontiguouscache.h.

References d, and Q_ASSERT.

◆ 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 178 of file qcontiguouscache.h.

References allocateData(), d, Q_ASSERT, and qMin().

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◆ 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 98 of file qcontiguouscache.h.

References d.

◆ 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 70 of file qcontiguouscache.h.

References d, other(), and qt_ptr_swap().

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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 428 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 432 of file qcontiguouscache.h.

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

qtbase/src/corelib/tools/qcontiguouscache.h (f3d0f4f4c37de11595122c589ec512d10aa7e94a)
qtbase/src/corelib/tools/qcontiguouscache.cpp (516aa662a06fd01e7caf23f282702465a23424b8)

Public Types

Public Member Functions

Detailed Description

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()