Performs the sorting by being a parent to ForClause. More...

#include <qorderby_p.h>

Inheritance diagram for QPatternist::OrderBy:

Classes
class	OrderSpec

Public Types
enum	Stability { StableOrder, UnstableOrder }

Public Types inherited from QPatternist::Expression
typedef QExplicitlySharedDataPointer< const Expression >	ConstPtr
	A smart pointer wrapping `const` Expression instances. More...

enum	ID { IDBooleanValue = 1, IDCountFN, IDEmptyFN, IDExistsFN, IDExpressionSequence, IDGeneralComparison, IDIfThenClause, IDIgnorableExpression, IDIntegerValue, IDPositionFN, IDStringValue, IDValueComparison, IDRangeVariableReference, IDContextItem, IDUserFunctionCallsite, IDExpressionVariableReference, IDAttributeConstructor, IDUpperCaseFN, IDLowerCaseFN, IDFirstItemPredicate, IDEmptySequence, IDReturnOrderBy, IDLetClause, IDForClause, IDPath, IDNamespaceConstructor, IDArgumentReference, IDGenericPredicate, IDAxisStep, IDFloat, IDCombineNodes, IDUnresolvedVariableReference, IDCardinalityVerifier }

typedef QList< Expression::Ptr >	List

typedef QFlags< Property >	Properties

enum	Property { UseContextItem = 1, DisableElimination = 1 << 1, IsEvaluated = 1 << 2, DisableTypingDeduction = 1 << 3, EmptynessFollowsChild = 1 << 4, RewriteToEmptyOnEmpty = 1 << 5, RequiresFocus = 1 << 6, AffectsOrderOnly = 1 << 7, RequiresContextItem = (1 << 8) \| RequiresFocus, CreatesFocusForLast = 1 << 9, LastOperandIsCollation = 1 << 10, DependsOnLocalVariable = (1 << 11) \| DisableElimination, EvaluationCacheRedundant = (1 << 12), IsNodeConstructor = 1 << 13, RequiresCurrentItem = 1 << 14 }

typedef QExplicitlySharedDataPointer< Expression >	Ptr
	A smart pointer wrapping mutable Expression instances. More...

typedef ::QAbstractXmlForwardIterator< Expression::Ptr >	QAbstractXmlForwardIterator

typedef QVector< Expression::Ptr >	Vector

Public Functions
virtual ExpressionVisitorResult::Ptr	accept (const ExpressionVisitor::Ptr &visitor) const

virtual Expression::Ptr	compress (const StaticContext::Ptr &context)

virtual Item::Iterator::Ptr	evaluateSequence (const DynamicContext::Ptr &context) const

virtual SequenceType::List	expectedOperandTypes () const

Item::Iterator::Ptr	mapToSequence (const Item &i, const DynamicContext::Ptr &context) const

	OrderBy (const Stability stability, const OrderSpec::Vector &orderSpecs, const Expression::Ptr &operand, ReturnOrderBy *const returnOrderBy)

virtual Properties	properties () const

virtual SequenceType::Ptr	staticType () const

virtual Expression::Ptr	typeCheck (const StaticContext::Ptr &context, const SequenceType::Ptr &reqType)

Public Functions inherited from QPatternist::SingleContainer
virtual bool	compressOperands (const StaticContext::Ptr &)

virtual Expression::List	operands () const

virtual void	setOperands (const Expression::List &operands)

Public Functions inherited from QPatternist::Expression
virtual const SourceLocationReflection *	actualReflection () const
	Returns `this`. More...

virtual void	announceFocusType (const ItemType::Ptr &itemType)

Properties	deepProperties () const
	Computes the union of properties for this Expression and all its descending children. More...

virtual Properties	dependencies () const

virtual QString	description () const

virtual bool	evaluateEBV (const DynamicContext::Ptr &context) const

virtual Item	evaluateSingleton (const DynamicContext::Ptr &context) const

virtual void	evaluateToSequenceReceiver (const DynamicContext::Ptr &context) const

virtual ItemType::Ptr	expectedContextItemType () const

	Expression ()

bool	has (const Property prop) const

bool	hasDependency (const Property prop) const

virtual ID	id () const

bool	is (const ID id) const

bool	isEvaluated () const

virtual ItemType::Ptr	newFocusType () const

virtual QList< QExplicitlySharedDataPointer< OptimizationPass > >	optimizationPasses () const

virtual PatternPriority	patternPriority () const

const Expression::Ptr &	rewrite (const Expression::Ptr &to, const StaticContext::Ptr &context) const
	Rewrites this Expression to `to`, and return `to`. More...

virtual	~Expression ()

Public Functions inherited from QSharedData
	QSharedData ()
	Constructs a QSharedData object with a reference count of 0. More...

	QSharedData (const QSharedData &)
	Constructs a QSharedData object with reference count 0. More...

Public Functions inherited from QPatternist::CppCastingHelper< Expression >
const TCastTarget *	as () const

TCastTarget *	as ()

Public Functions inherited from QPatternist::SourceLocationReflection
virtual QSourceLocation	sourceLocation () const

	SourceLocationReflection ()

virtual	~SourceLocationReflection ()

Private Types
typedef QExplicitlySharedDataPointer< const OrderBy >	ConstPtr

Properties
OrderSpec::Vector	m_orderSpecs

ReturnOrderBy *const	m_returnOrderBy

const Stability	m_stability

Additional Inherited Members
Static Public Functions inherited from QPatternist::Expression
static void	rewrite (Expression::Ptr &old, const Expression::Ptr &New, const StaticContext::Ptr &context)

Public Variables inherited from QSharedData
QAtomicInt	ref

Protected Functions inherited from QPatternist::SingleContainer
	SingleContainer (const Expression::Ptr &operand)

Protected Functions inherited from QPatternist::Expression
void	typeCheckOperands (const StaticContext::Ptr &context)

Protected Functions inherited from QPatternist::CppCastingHelper< Expression >
	CppCastingHelper ()

Protected Variables inherited from QPatternist::SingleContainer
Expression::Ptr	m_operand

Detailed Description

Performs the sorting by being a parent to ForClause.

The child of the ForClause is a ReturnOrderBy expression, which collects the sort keys and values.

Author: Frans Englich frans.nosp@m..eng.nosp@m.lich@.nosp@m.noki.nosp@m.a.com

Definition at line 76 of file qorderby_p.h.

Typedefs

◆ ConstPtr

typedef QExplicitlySharedDataPointer<const OrderBy> QPatternist::OrderBy::ConstPtr

private

Needed when calling makeSequenceMappingIterator().

Definition at line 168 of file qorderby_p.h.

Enumerations

◆ Stability

enum QPatternist::OrderBy::Stability

Enumerator
StableOrder
UnstableOrder

Definition at line 79 of file qorderby_p.h.

         {
             StableOrder,
             UnstableOrder
         };

Constructors and Destructors

◆ OrderBy()

OrderBy::OrderBy	(	const Stability	stability,
		const OrderSpec::Vector &	orderSpecs,
		const Expression::Ptr &	operand,
		ReturnOrderBy *const	returnOrderBy
	)

Definition at line 58 of file qorderby.cpp.

Referenced by QPatternist::OrderBy::OrderSpec::operatorID().

                                                      : SingleContainer(op)
                                                      , m_stability(stability)
                                                      , m_orderSpecs(aOrderSpecs)
                                                      , m_returnOrderBy(returnOrderBy)
 {
     Q_ASSERT(m_returnOrderBy);
 }

Functions

◆ accept()

ExpressionVisitorResult::Ptr OrderBy::accept ( const ExpressionVisitor::Ptr & visitor ) const

virtual

Implements QPatternist::Expression.

Definition at line 256 of file qorderby.cpp.

Referenced by QPatternist::OrderBy::OrderSpec::operatorID().

 {
     return visitor->visit(this);
 }

◆ compress()

Expression::Ptr OrderBy::compress ( const StaticContext::Ptr & context )

virtual

compress() is the last stage performs in compiling an expression, done after the initial AST build and calling typeCheck(). compress() performs crucial simplifications, either by having drastic performance implications or that some expressions depend on it for proper behavior.

The default implementation performs a sparse conditional constant propagation. In short, a recursive process is performed in the AST which examines if the Expression's operands are constant values, and if so, performs a const fold(AST rewrite) into the result of evaluating the expression in question. This default behavior can be disabled by letting properties() return DisableElimination.

This compress() stage can be relative effective due to the design of XPath, in part because intrinsic functions are heavily used. Many Expressions override compress() and do optimizations specific to what they do. Also, many Expressions performs optimizations in their typeCheck().

Parameters

context the static context. Supplies compile time information, and is the channel for communicating error messages.

See also: Wikipedia, the free encyclopedia, Sparse conditional constant propagation; Wikipedia, the free encyclopedia, Intrinsic function; Wikipedia, the free encyclopedia, Compiler optimization

Reimplemented from QPatternist::Expression.

Definition at line 231 of file qorderby.cpp.

Referenced by QPatternist::OrderBy::OrderSpec::operatorID().

 {
     /* If we only will produce one item, there's no point in sorting. */
     if(m_operand->staticType()->cardinality().allowsMany())
         return SingleContainer::compress(context);
     else
     {
         m_returnOrderBy->setStay(false);
         return m_operand->compress(context);
     }
 }

◆ evaluateSequence()

Item::Iterator::Ptr OrderBy::evaluateSequence ( const DynamicContext::Ptr & context ) const

virtual

Evaluate this Expression by iterating over it. This is a central function for evaluating expressions.

Expressions must always always return a valid QAbstractXmlForwardIterator and may never return 0. If an empty result is of interest to be returned, the EmptyIterator should be returned.

The default implementation returns a SingletonIterator over the item returned from evaluateSingleton().

Note: This function may raise an exception when calling, not only when QAbstractXmlForwardIterator::next() is called on the return value. This is because in some cases evaluateSingleton() is called directly.

Reimplemented from QPatternist::Expression.

Definition at line 174 of file qorderby.cpp.

Referenced by QPatternist::OrderBy::OrderSpec::operatorID().

 {
     Item::List tuples(m_operand->evaluateSequence(context)->toList());
 
     const qLess<Item::List> sorter(m_orderSpecs, context);
 
     Q_ASSERT(m_stability == StableOrder || m_stability == UnstableOrder);
 
     /* On one hand we could just disregard stability and always use qStableSort(), but maybe qSort()
      * is a bit faster? */
     if(m_stability == StableOrder)
         qStableSort(tuples.begin(), tuples.end(), sorter);
     else
     {
         Q_ASSERT(m_stability == UnstableOrder);
         qSort(tuples.begin(), tuples.end(), sorter);
     }
 
     return makeSequenceMappingIterator<Item>(ConstPtr(this),
                                              makeListIterator(tuples),
                                              context);
 }

◆ expectedOperandTypes()

SequenceType::List OrderBy::expectedOperandTypes ( ) const

virtual

Returns a list of Sequence Types, describing the type of each of the expression's operands. Hence, this function has a relationship to the operands() function:

- The lengths of the lists returned by expectedOperandTypes()
and operands() should always be equal in length, since one
cannot describe the type of a non-existent operand(and all
operands must have type information).
- A significant difference between the two functions is that while
the type of objects in the list returned by operands() may vary
between compilations/static context, simply because the particular
Expression is part of different XPath expressions, the
types in the list returned by expectedOperandTypes is always the same
since the function/operator signature never changes.

This function should not be confused with staticType(), which returns the static type of the expression itself, not its operands. The function call is an expression where this is clear: the type of the return value is not the same as the arguments' types. The static type of the operands supplied to the expression can be determined via the staticType() function of the instances returned by operands().

If the expression has no operands, an empty list should be returned.

Implements QPatternist::Expression.

Definition at line 248 of file qorderby.cpp.

Referenced by QPatternist::OrderBy::OrderSpec::operatorID().

 {
     SequenceType::List result;
     result.append(CommonSequenceTypes::ZeroOrMoreItems);
     return result;
 }

◆ mapToSequence()

Item::Iterator::Ptr OrderBy::mapToSequence	(	const Item &	i,
		const DynamicContext::Ptr &	context
	)		const

inline

Definition at line 168 of file qorderby.cpp.

Referenced by QPatternist::OrderBy::OrderSpec::operatorID().

 {
     return i.as<SortTuple>()->value();
 }

◆ properties()

Expression::Properties OrderBy::properties ( ) const

virtual

Returns: a bitwise OR'd value of properties, describing the characteristics of the expression. These properties affects how this Expression is treated in for example type checking stages.

The default implementation returns 0. Override and let the function return a different value, if that's of interest.

An important decision when re-implementing properties() is whether to OR in the properties() of ones operands. For instance, if an operand has RequiresFocus set, that flag nost likely applies to the apparent as well, since it depends on its operand.

See also: deepProperties()

Returns: Expression::None, meaning no special properties

Reimplemented from QPatternist::Expression.

Definition at line 226 of file qorderby.cpp.

Referenced by QPatternist::OrderBy::OrderSpec::operatorID().

 {
     return m_operand->properties() & DisableElimination;
 }

◆ staticType()

SequenceType::Ptr OrderBy::staticType ( ) const

virtual

Returns: the static type of this Expression. For example, an 'and' expression have as static type xs:boolean

Implements QPatternist::Expression.

Definition at line 243 of file qorderby.cpp.

Referenced by QPatternist::OrderBy::OrderSpec::operatorID().

 {
     return m_operand->staticType();
 }

◆ typeCheck()

Expression::Ptr OrderBy::typeCheck	(	const StaticContext::Ptr &	context,
		const SequenceType::Ptr &	reqType
	)

virtual

This implementation guarantees to never rewrite away this Expression, but at most rewrite it as a child of another expression(that presumably have a type checking role). It is therefore always safe to override this function and call this implementation and not worry about that this Expression becomes deleted.

Many Expressions override typeCheck() and performs optimizations, as opposed to doing it in the compress() stage. This is due to that the design of those Expressions often are tied to that certain simplifications are done at the typeCheck() stage of the compilation process or that it in some other way is related to what the typeCheck() do. Also, the earlier the AST can be simplified, the better the chances are for subsequent optimizations.

It is important that the super class's typeCheck() is called before doing any custom type checking, since the call can change the children(notably, the childrens' static types). For example, if the Expression, MyExpression in the example, does not match the required type, typeCheck returns the Expression wrapped in for example ItemVerifier, CardinalityVerifier, or both.

typeCheck() may be called many times. typeCheck() must either raise an error if this Expression is an invalid expression. Thus, it is guaranteed that an Expression is valid after typeCheck() is called.

Parameters

context	supplies information, such as namespace bindings and available function signatures, that can be needed at compilation time. `context` is guaranteed by the caller to never null.
reqType	the static type that this Expression must match when evaluated. `reqType` is guaranteed by the caller to never null.

Returns: an Expression that can be this Expression, or another expression, which somehow is necessary for making this Expression conforming to reqType

Reimplemented from QPatternist::Expression.

Definition at line 197 of file qorderby.cpp.

Referenced by QPatternist::OrderBy::OrderSpec::operatorID().

 {
     m_returnOrderBy->setStay(true);
 
     /* It's important we do the typeCheck() before calling OrderSpec::prepare(), since
      * atomizers must first be inserted. */
     const Expression::Ptr me(SingleContainer::typeCheck(context, reqType));
 
     const Expression::List ops(m_returnOrderBy->operands());
     const int len = ops.count();
     Q_ASSERT(ops.count() > 1);
     Q_ASSERT(m_orderSpecs.count() == ops.count() - 1);
 
     for(int i = 1; i < len; ++i)
         m_orderSpecs[i - 1].prepare(ops.at(i), context);
 
     return me;
 
     /* It's not meaningful to sort a single item or less, so rewrite ourselves
      * away if that is the case. This is an optimization. */
     /* TODO: How do we remove ReturnOrderBy?
     if(Cardinality::zeroOrOne().isMatch(m_operand->staticType()->cardinality()))
         return m_operand->typeCheck(context, reqType);
     else
         return SingleContainer::typeCheck(context, reqType);
      */
 }

Properties

◆ m_orderSpecs

OrderSpec::Vector QPatternist::OrderBy::m_orderSpecs

private

Definition at line 171 of file qorderby_p.h.

Referenced by evaluateSequence(), qLess< Item::List >::operator()(), qLess< Item::List >::qLess(), and typeCheck().

◆ m_returnOrderBy

ReturnOrderBy* const QPatternist::OrderBy::m_returnOrderBy

private

Definition at line 172 of file qorderby_p.h.

Referenced by compress(), OrderBy(), and typeCheck().

◆ m_stability

const Stability QPatternist::OrderBy::m_stability

private

Definition at line 170 of file qorderby_p.h.

Referenced by evaluateSequence().

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

/src/xmlpatterns/expr/qorderby_p.h
/src/xmlpatterns/expr/qorderby.cpp

Classes

Public Types

Public Functions

Private Types

Properties

Additional Inherited Members

Detailed Description

Typedefs

◆ ConstPtr

Enumerations

◆ Stability

Constructors and Destructors

◆ OrderBy()

Functions

◆ accept()

◆ compress()

◆ evaluateSequence()

◆ expectedOperandTypes()

◆ mapToSequence()

◆ properties()

◆ staticType()

◆ typeCheck()

Properties

◆ m_orderSpecs

◆ m_returnOrderBy

◆ m_stability