Implements the comma(",") operator, the sequence constructor. More...

#include <qexpressionsequence_p.h>

Inheritance diagram for QPatternist::ExpressionSequence:

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 &) const

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

virtual SequenceType::List	expectedOperandTypes () const

	ExpressionSequence (const Expression::List &operands)

virtual ID	id () const

Item::Iterator::Ptr	mapToSequence (const Expression::Ptr &, const DynamicContext::Ptr &) const

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

virtual Item	evaluateSingleton (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 ()

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 ExpressionSequence >	ConstPtr

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

Implements the comma(",") operator, the sequence constructor.

For example, the expression alpha, beta evaluates to a sequence containing the items the nodetest alpha evaluates to, concatenated with the items the nodetest beta evaluates to.

See also: XML Path Language (XPath) 2.0, 3.3.1 Constructing Sequences

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

Definition at line 75 of file qexpressionsequence_p.h.

Typedefs

◆ ConstPtr

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

private

Definition at line 119 of file qexpressionsequence_p.h.

Constructors and Destructors

◆ ExpressionSequence()

ExpressionSequence::ExpressionSequence ( const Expression::List & operands )

Creates an ExpressionSequence with the operands operands. operands must contain two or more Expression instances.

Definition at line 53 of file qexpressionsequence.cpp.

                                                                 : UnlimitedContainer(ops)
 {
     Q_ASSERT_X(1 < ops.count(), Q_FUNC_INFO,
                "It makes no sense to have an ExpressionSequence containing less than two expressions.");
 }

Functions

◆ accept()

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

virtual

Implements QPatternist::Expression.

Definition at line 196 of file qexpressionsequence.cpp.

 {
     return visitor->visit(this);
 }

◆ compress()

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

virtual

Removes any empty sequences, typically "()", from its list of children. If after that rewrite has no children, it rewrites itself to the CommonValues::empty; if it has only one, it rewrites to the child.

This optimization is not very usable by itself, but potentially becomes effective after other optimizations have rewritten themselves into empty sequences. Thus, saving memory consumption and runtime overhead.

Reimplemented from QPatternist::Expression.

Definition at line 82 of file qexpressionsequence.cpp.

 {
     const Expression::Ptr me(UnlimitedContainer::compress(context));
 
     if(me != this)
         return me;
 
     Expression::List::const_iterator it(m_operands.constBegin());
     const Expression::List::const_iterator end(m_operands.constEnd());
     Expression::List result;
 
     for(; it != end; ++it)
     {
         const ID Id = (*it)->id();
 
         /* Remove empty sequences. This is rather important because we have some steps in the parser that
          * intentionally, unconditionally and for temporary reasons create expressions like (expr, ()). Of course,
          * empty sequences also occur as part of optimizations.
          *
          * User function call sites that are of type empty-sequence() must be avoided since
          * they may contain calls to fn:error(), which we would rewrite away otherwise. */
         if(Id != IDUserFunctionCallsite && (*it)->staticType()->cardinality().isEmpty())
         {
             /* Rewrite "(1, (), 2)" into "(1, 2)" by not
              * adding (*it) to result. */
             continue;
         }
         else if(Id == IDExpressionSequence)
         {
             /* Rewrite "(1, (2, 3), 4)" into "(1, 2, 3, 4)" */
             Expression::List::const_iterator seqIt((*it)->operands().constBegin());
             const Expression::List::const_iterator seqEnd((*it)->operands().constEnd());
 
             for(; seqIt != seqEnd; ++seqIt)
                 result.append(*seqIt);
         }
         else
             result.append(*it);
     }
 
     if(result.isEmpty())
         return EmptySequence::create(this, context);
     else if(result.count() == 1)
         return result.first();
     else
     {
         m_operands = result;
         return me;
     }
 }

◆ evaluateSequence()

Item::Iterator::Ptr ExpressionSequence::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 65 of file qexpressionsequence.cpp.

 {
     return makeSequenceMappingIterator<Item>(ConstPtr(this),
                                              makeListIterator(m_operands),
                                              context);
 }

◆ evaluateToSequenceReceiver()

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

virtual

Forwards the call to its children.

Reimplemented from QPatternist::Expression.

Definition at line 72 of file qexpressionsequence.cpp.

 {
     Expression::List::const_iterator it(m_operands.constBegin());
     const Expression::List::const_iterator end(m_operands.constEnd());
     Expression::List result;
 
     for(; it != end; ++it)
         (*it)->evaluateToSequenceReceiver(context);
 }

◆ expectedOperandTypes()

SequenceType::List ExpressionSequence::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 187 of file qexpressionsequence.cpp.

 {
     SequenceType::List result;
     /* ExpressionSequence is a bit strange type wise since it has an
      * infinite amount of operands. */
     result.append(CommonSequenceTypes::ZeroOrMoreItems);
     return result;
 }

◆ id()

Expression::ID ExpressionSequence::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 201 of file qexpressionsequence.cpp.

 {
     return IDExpressionSequence;
 }

◆ mapToSequence()

Item::Iterator::Ptr ExpressionSequence::mapToSequence	(	const Expression::Ptr &	expr,
		const DynamicContext::Ptr &	context
	)		const

inline

Definition at line 59 of file qexpressionsequence.cpp.

 {
     return expr->evaluateSequence(context);
 }

◆ properties()

Expression::Properties ExpressionSequence::properties ( ) const

virtual

Returns: Expression::DisableElimination, plus the union of all this ExpressionSequence's children's properties. If any child does not have IsEvaluated, it is removed from the result.

Reimplemented from QPatternist::Expression.

Definition at line 155 of file qexpressionsequence.cpp.

 {
     const Expression::List::const_iterator end(m_operands.constEnd());
     Expression::List::const_iterator it;
     bool allEvaled = true;
     Expression::Properties props(DisableElimination); /* Why do we have this flag? */
 
     for(it = m_operands.constBegin(); it != end; ++it)
     {
         const Expression::Properties newp((*it)->properties());
         props |= newp;
 
         if((newp & IsEvaluated) != IsEvaluated)
         {
             allEvaled = false;
             break;
         }
     }
 
     if(!allEvaled)
         props &= ~IsEvaluated; /* Remove IsEvaluated. */
 
     /* One of our children might need the focus, but we don't, so
      * cut it out. */
     return props & ~RequiresFocus;
 }

◆ staticType()

SequenceType::Ptr ExpressionSequence::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 182 of file qexpressionsequence.cpp.

 {
     return operandsUnionType<ProductOfCardinality>();
 }

◆ typeCheck()

Expression::Ptr ExpressionSequence::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 133 of file qexpressionsequence.cpp.

 {
     Q_ASSERT(reqType);
     Expression::List::iterator it(m_operands.begin());
     const Expression::List::iterator end(m_operands.end());
 
     /* We treat the cardinality differently here by allowing the empty sequence
      * for each individual Expression, since the Cardinality can be conformed to by
      * the ExpressionSequence as a whole(which we check for at the end). */
     const SequenceType::Ptr testOnlyIT(makeGenericSequenceType(reqType->itemType(),
                                                                Cardinality::empty() |
                                                                reqType->cardinality()));
 
     for(; it != end; ++it)
         *it = (*it)->typeCheck(context, testOnlyIT);
 
     /* The above loop is only guaranteed to find item type errors, but the cardinality
      * can still be wrong since the operands were treated individually. */
     return CardinalityVerifier::verifyCardinality(Expression::Ptr(this), reqType->cardinality(), context);
 }

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

/src/xmlpatterns/expr/qexpressionsequence_p.h
/src/xmlpatterns/expr/qexpressionsequence.cpp

Public Functions

Private Types

Additional Inherited Members

Detailed Description

Typedefs

◆ ConstPtr

Constructors and Destructors

◆ ExpressionSequence()

Functions

◆ accept()

◆ compress()

◆ evaluateSequence()

◆ evaluateToSequenceReceiver()

◆ expectedOperandTypes()

◆ id()

◆ mapToSequence()

◆ properties()

◆ staticType()

◆ typeCheck()