Implements XPath 2.0's operators for combining node sequences: union, intersect and except. More...

#include <qcombinenodes_p.h>

Inheritance diagram for QPatternist::CombineNodes:

Public Types
enum	Operator { Union = 1, Intersect = 2, Except = 4 }

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

	CombineNodes (const Expression::Ptr &operand1, const Operator op, const Expression::Ptr &operand2)

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

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

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

virtual SequenceType::List	expectedOperandTypes () const

virtual ID	id () const

Operator	operatorID () const

virtual SequenceType::Ptr	staticType () const

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

Public Functions inherited from QPatternist::PairContainer
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)

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

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 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

virtual Properties	properties () 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 ()

Static Public Functions
static QString	displayName (const Operator op)

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

Properties
const Operator	m_operator

Additional Inherited Members
Public Variables inherited from QSharedData
QAtomicInt	ref

Protected Functions inherited from QPatternist::PairContainer
	PairContainer (const Expression::Ptr &operand1, const Expression::Ptr &operand2)

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::PairContainer
Expression::Ptr	m_operand1

Expression::Ptr	m_operand2

Detailed Description

Implements XPath 2.0's operators for combining node sequences: union, intersect and except.

See also: XQuery 1.0: An XML Query Language, 3.3.3 Combining QXmlNodeModelIndex Sequences

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

Definition at line 72 of file qcombinenodes_p.h.

Enumerations

◆ Operator

enum QPatternist::CombineNodes::Operator

Enumerator
Union
Intersect
Except

Definition at line 75 of file qcombinenodes_p.h.

         {
             Union       = 1,
             Intersect   = 2,
             Except      = 4
         };

Constructors and Destructors

◆ CombineNodes()

CombineNodes::CombineNodes	(	const Expression::Ptr &	operand1,
		const Operator	op,
		const Expression::Ptr &	operand2
	)

Definition at line 56 of file qcombinenodes.cpp.

                                                           : PairContainer(operand1, operand2),
                                                               m_operator(op)
 {
     Q_ASSERT(op == Union    ||
              op == Except   ||
              op == Intersect);
 }

Functions

◆ accept()

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

virtual

Implements QPatternist::Expression.

Definition at line 162 of file qcombinenodes.cpp.

 {
     return visitor->visit(this);
 }

◆ displayName()

QString CombineNodes::displayName ( const Operator op )

static

Determines the string representation for operator op.

Returns: "union" if op is Union, "intersect" if op is Intersect and "except" if op is Except.

Definition at line 116 of file qcombinenodes.cpp.

 {
     switch(op)
     {
         case Intersect:
             return QLatin1String("intersect");
         case Except:
             return QLatin1String("except");
         default:
         {
             Q_ASSERT(op == Union);
             return QLatin1String("union");
         }
     }
 }

◆ evaluateEBV()

bool CombineNodes::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 102 of file qcombinenodes.cpp.

 {
     /* If it's the union operator, we can possibly avoid
      * evaluating the second operand. */
 
     if(m_operator == Union)
     {
         return m_operand1->evaluateEBV(context) ||
                m_operand2->evaluateEBV(context);
     }
     else
         return PairContainer::evaluateEBV(context);
 }

◆ evaluateSequence()

Item::Iterator::Ptr CombineNodes::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 66 of file qcombinenodes.cpp.

Referenced by evaluateSingleton().

 {
     const Item::Iterator::Ptr op1(m_operand1->evaluateSequence(context));
     const Item::Iterator::Ptr op2(m_operand2->evaluateSequence(context));
 
     switch(m_operator)
     {
         case Intersect:
             return Item::Iterator::Ptr(new IntersectIterator(op1, op2));
         case Except:
             return Item::Iterator::Ptr(new ExceptIterator(op1, op2));
         default:
         {
             Q_ASSERT(m_operator == Union);
             return Item::Iterator::Ptr(new UnionIterator(op1, op2));
         }
     }
 }

◆ evaluateSingleton()

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

virtual

Reimplemented from QPatternist::Expression.

Definition at line 85 of file qcombinenodes.cpp.

 {
     return evaluateSequence(context)->next();
 }

◆ expectedOperandTypes()

SequenceType::List CombineNodes::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 149 of file qcombinenodes.cpp.

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

◆ id()

Expression::ID CombineNodes::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 167 of file qcombinenodes.cpp.

 {
     return IDCombineNodes;
 }

◆ operatorID()

CombineNodes::Operator CombineNodes::operatorID ( ) const

Definition at line 157 of file qcombinenodes.cpp.

 {
     return m_operator;
 }

◆ staticType()

SequenceType::Ptr CombineNodes::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 132 of file qcombinenodes.cpp.

 {
     const SequenceType::Ptr t1(m_operand1->staticType());
     const SequenceType::Ptr t2(m_operand2->staticType());
 
      Cardinality card;
 
      /* Optimization: the cardinality can be better inferred for
       * Intersect and Except, although it's not trivial code. */
      if(m_operator == Union)
          card = t1->cardinality() | t2->cardinality();
      else /* Except. */
          card = Cardinality::zeroOrMore();
 
      return makeGenericSequenceType(t1->itemType() | t2->itemType(), card);
 }

◆ typeCheck()

Expression::Ptr CombineNodes::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 90 of file qcombinenodes.cpp.

 {
 
     const Expression::Ptr me(PairContainer::typeCheck(context, reqType));
 
     m_operand1 = NodeSortExpression::wrapAround(m_operand1, context);
     m_operand2 = NodeSortExpression::wrapAround(m_operand2, context);
 
     return me;
 }

Properties

◆ m_operator

const Operator QPatternist::CombineNodes::m_operator

private

Definition at line 108 of file qcombinenodes_p.h.

Referenced by evaluateEBV(), evaluateSequence(), operatorID(), and staticType().

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

/src/xmlpatterns/expr/qcombinenodes_p.h
/src/xmlpatterns/expr/qcombinenodes.cpp

Public Types

Public Functions

Static Public Functions

Properties

Additional Inherited Members

Detailed Description

Enumerations

◆ Operator

Constructors and Destructors

◆ CombineNodes()

Functions

◆ accept()

◆ displayName()

◆ evaluateEBV()

◆ evaluateSequence()

◆ evaluateSingleton()

◆ expectedOperandTypes()

◆ id()

◆ operatorID()

◆ staticType()

◆ typeCheck()

Properties

◆ m_operator