Together with OrderBy, it implements XQuery 1.0's order by expression. More...

#include <qreturnorderby_p.h>

Inheritance diagram for QPatternist::ReturnOrderBy:

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

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

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

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

virtual SequenceType::List	expectedOperandTypes () const

virtual ID	id () const

OrderBy::OrderSpec::Vector	orderSpecs () const

virtual Properties	properties () const

	ReturnOrderBy (const OrderBy::Stability stability, const OrderBy::OrderSpec::Vector &oSpecs, const Expression::List &operands)

void	setStay (const bool a)

OrderBy::Stability	stability () const

virtual SequenceType::Ptr	staticType () const

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

virtual Expression::List	operands () const

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

	UnlimitedContainer (const Expression::List &operands=Expression::List())

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 Item::Iterator::Ptr	evaluateSequence (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

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

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 ()

Properties
bool	m_flyAway

OrderBy::OrderSpec::Vector	m_orderSpecs

const OrderBy::Stability	m_stability

Additional Inherited Members
Public Types inherited from QPatternist::UnlimitedContainer
enum	CardinalityComputation { ProductOfCardinality, UnionOfCardinality }

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

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::UnlimitedContainer
template<CardinalityComputation suppliedCard>
SequenceType::Ptr	operandsUnionType () const

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::UnlimitedContainer
Expression::List	m_operands

Detailed Description

Together with OrderBy, it implements XQuery 1.0's order by expression.

ReturnOrderBy evaluates the sort keys and values, and hands it over to OrderBy, which is an AST ancestor, using SortTuples.

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

Definition at line 73 of file qreturnorderby_p.h.

Constructors and Destructors

◆ ReturnOrderBy()

ReturnOrderBy::ReturnOrderBy	(	const OrderBy::Stability	stability,
		const OrderBy::OrderSpec::Vector &	oSpecs,
		const Expression::List &	operands
	)

In operands the first item is the return expression, and the rest, which is at least one, are the sort keys.

Definition at line 52 of file qreturnorderby.cpp.

                                                         : UnlimitedContainer(ops)
                                                           , m_stability(aStability)
                                                           , m_orderSpecs(oSpecs)
                                                           , m_flyAway(true)
 {
     Q_ASSERT_X(m_operands.size() >= 2, Q_FUNC_INFO,
                "ReturnOrderBy must have the return expression, and at least one sort key.");
     Q_ASSERT(m_orderSpecs.size() == ops.size() - 1);
 }

Functions

◆ accept()

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

virtual

Implements QPatternist::Expression.

Definition at line 110 of file qreturnorderby.cpp.

 {
     return visitor->visit(this);
 }

◆ compress()

Expression::Ptr ReturnOrderBy::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 86 of file qreturnorderby.cpp.

 {
     /* We first did this in typeCheck(), but that broke due to that type checks were
      * missed, which other pieces relied on. */
     if(m_flyAway)
     {
         /* We only want the return expression, not the sort keys. */
         return m_operands.first()->compress(context);
     }
     else
     {
         /* We don't need the members, so don't keep a reference to them. */
         m_orderSpecs.clear();
 
         return UnlimitedContainer::compress(context);
     }
 }

◆ evaluateEBV()

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

virtual

Determines the Effective Boolean Value of the expression.

The Effective Boolean Value of a value is not necessarily the same as converting the value to a new value of type xs:boolean.

Note that this function cannot return the empty sequence, evaluateSingleton() must be overridden in order to be able to do that.

The default implementation results in a type error. Hence, this function must be overridden if such behavior is not of interest.

See also: XML Path Language (XPath) 2.0, 2.4.3 Effective Boolean Value

Reimplemented from QPatternist::Expression.

Definition at line 80 of file qreturnorderby.cpp.

 {
     // TODO This is temporary code.
     return m_operands.first()->evaluateEBV(context);
 }

◆ evaluateSingleton()

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

virtual

Reimplemented from QPatternist::Expression.

Definition at line 64 of file qreturnorderby.cpp.

 {
     Q_ASSERT(m_operands.size() > 1);
     const Item::Iterator::Ptr value(makeListIterator(m_operands.first()->evaluateSequence(context)->toList()));
     Item::Vector sortKeys;
 
     /* We're skipping the first operand. */
     const int len = m_operands.size() - 1;
     sortKeys.resize(len);
 
     for(int i = 1; i <= len; ++i)
         sortKeys[i - 1] = m_operands.at(i)->evaluateSingleton(context);
 
     return Item(new SortTuple(value, sortKeys));
 }

◆ expectedOperandTypes()

SequenceType::List ReturnOrderBy::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 120 of file qreturnorderby.cpp.

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

◆ id()

Expression::ID ReturnOrderBy::id ( ) const

virtual

This property, which has no setter, returns an enum value that uniquely identifies this Expression. Patternist makes no use of C++'s dynamic_cast feature, but uses this polymorphic function instead.

Returns: always IgnorableExpression.

Reimplemented from QPatternist::Expression.

Definition at line 128 of file qreturnorderby.cpp.

 {
     return IDReturnOrderBy;
 }

◆ orderSpecs()

OrderBy::OrderSpec::Vector QPatternist::ReturnOrderBy::orderSpecs ( ) const

inline

Definition at line 92 of file qreturnorderby_p.h.

Referenced by QPatternist::yyparse().

         {
             return m_orderSpecs;
         }

◆ properties()

Expression::Properties ReturnOrderBy::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 104 of file qreturnorderby.cpp.

Referenced by setStay().

 {
     /* For some unknown reason this is necessary for XQTS test case orderBy18. */
     return DisableElimination;
 }

◆ setStay()

void QPatternist::ReturnOrderBy::setStay ( const bool a )

inline

In the case of that we don't have a for-expression beloning us, but only a let clause, this ReturnOrderBy breaks if it stays in the AST. So, by default we assume that we should write ourselves away, unless this function is called. The associated ForClause will call it during typeCheck(), if it exists.

Definition at line 109 of file qreturnorderby_p.h.

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

         {
             m_flyAway = !a;
         }

◆ stability()

OrderBy::Stability QPatternist::ReturnOrderBy::stability ( ) const

inline

Definition at line 97 of file qreturnorderby_p.h.

Referenced by QPatternist::yyparse().

         {
             return m_stability;
         }

◆ staticType()

SequenceType::Ptr ReturnOrderBy::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 115 of file qreturnorderby.cpp.

 {
     return m_operands.first()->staticType();
 }

Properties

◆ m_flyAway

bool QPatternist::ReturnOrderBy::m_flyAway

private

See also: stay()

Definition at line 128 of file qreturnorderby_p.h.

Referenced by compress(), and setStay().

◆ m_orderSpecs

OrderBy::OrderSpec::Vector QPatternist::ReturnOrderBy::m_orderSpecs

private

Definition at line 123 of file qreturnorderby_p.h.

Referenced by compress(), orderSpecs(), and ReturnOrderBy().

◆ m_stability

const OrderBy::Stability QPatternist::ReturnOrderBy::m_stability

private

This variable is unfortunately only used at compile time. However, it's tricky to get rid of it due to how QueryTransformParser would have to be adapted.

Definition at line 121 of file qreturnorderby_p.h.

Referenced by stability().

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

/src/xmlpatterns/expr/qreturnorderby_p.h
/src/xmlpatterns/expr/qreturnorderby.cpp

Public Functions

Properties

Additional Inherited Members

Detailed Description

Constructors and Destructors

◆ ReturnOrderBy()

Functions

◆ accept()

◆ compress()

◆ evaluateEBV()

◆ evaluateSingleton()

◆ expectedOperandTypes()

◆ id()

◆ orderSpecs()

◆ properties()

◆ setStay()

◆ stability()

◆ staticType()

Properties

◆ m_flyAway

◆ m_orderSpecs

◆ m_stability