Implements the function fn:subsequence(). More...

#include <qsequencefns_p.h>

Inheritance diagram for QPatternist::SubsequenceFN:

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

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

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

virtual SequenceType::Ptr	staticType () const

	SubsequenceFN ()

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

Public Functions inherited from QPatternist::FunctionCall
virtual ExpressionVisitorResult::Ptr	accept (const ExpressionVisitor::Ptr &visitor) const

virtual SequenceType::List	expectedOperandTypes () const

virtual ID	id () const

virtual Expression::Properties	properties () const

virtual void	setSignature (const FunctionSignature::Ptr &sign)

virtual FunctionSignature::Ptr	signature () 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 bool	evaluateEBV (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 ()

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_hasTypeChecked

Additional Inherited Members
Public Types inherited from QPatternist::FunctionCall
typedef QExplicitlySharedDataPointer< FunctionCall >	Ptr

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 function fn:subsequence().

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

Definition at line 310 of file qsequencefns_p.h.

Constructors and Destructors

◆ SubsequenceFN()

SubsequenceFN::SubsequenceFN ( )

Definition at line 216 of file qsequencefns.cpp.

                              : m_hasTypeChecked(false)
 {
 }

Functions

◆ compress()

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

virtual

This function implements rewrites the SubsequenceFN instance into an empty sequence if its third argument, the sequence length argument, is evaluated and is effectively equal or less than zero.

Reimplemented from QPatternist::Expression.

Definition at line 257 of file qsequencefns.cpp.

 {
     const Expression::Ptr me(FunctionCall::compress(context));
     if(me != this)
         return me;
 
     const Expression::Ptr lenArg(m_operands.value(2));
     if(lenArg && lenArg->isEvaluated())
     {
         const xsInteger length = lenArg->as<Literal>()->item().as<Numeric>()->round()->toInteger();
 
         if(length <= 0)
             return EmptySequence::create(this, context);
     }
 
     return me;
 }

◆ evaluateSequence()

Item::Iterator::Ptr SubsequenceFN::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 227 of file qsequencefns.cpp.

Referenced by evaluateSingleton().

 {
     Item::Iterator::Ptr it(m_operands.first()->evaluateSequence(context));
 
     xsInteger startingLoc = m_operands.at(1)->evaluateSingleton(context).as<Numeric>()->round()->toInteger();
     xsInteger length = -1;
 
     if(m_operands.count() == 3)
     {
         length = m_operands.last()->evaluateSingleton(context).as<Numeric>()->toInteger();
 
         if(startingLoc + length < 1 || (startingLoc > (startingLoc + length)))
             return CommonValues::emptyIterator;
     }
 
     /* F&O, 15.1.10, "If $startingLoc is zero or negative, the
      * subsequence includes items from the beginning of the $sourceSeq." */
     if(startingLoc < 1)
         startingLoc = 1;
 
     if(length < 1 && length != -1)
         return CommonValues::emptyIterator;
     return Item::Iterator::Ptr(new SubsequenceIterator(it, startingLoc, length));
 }

◆ evaluateSingleton()

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

virtual

Reimplemented from QPatternist::Expression.

Definition at line 252 of file qsequencefns.cpp.

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

◆ staticType()

SequenceType::Ptr SubsequenceFN::staticType ( ) const

virtual

Partially implements the static type inference rules.

See also: XQuery 1.0 and XPath 2.0 Formal Semantics, 7.2.13 The fn:subsequence function

Reimplemented from QPatternist::FunctionCall.

Definition at line 275 of file qsequencefns.cpp.

 {
     const SequenceType::Ptr opType(m_operands.first()->staticType());
     const Cardinality opCard(opType->cardinality());
 
     /* Optimization: we can do much stronger inference here. If the length is a
      * constant, we can constrain the range at least upwards of the
      * cardinality, for instance. */
 
     /* The subsequence(expr, 1, 1), add empty-sequence() to the static type.
      *
      * Note that we cannot do all these inferences before we've typechecked our
      * operands. The only known case of where our staticType() is called before
      * typeCheck() is through xmlpatternsview, although it wouldn't be
      * surprising if the more exotic paths can achieve that too.
      */
     if(m_hasTypeChecked &&
        m_operands.at(1)->isEvaluated()                                                      &&
        m_operands.count() == 3                                                              &&
        m_operands.at(2)->isEvaluated()                                                      &&
        m_operands.at(1)->as<Literal>()->item().as<Numeric>()->round()->toInteger() == 1     &&
        m_operands.at(2)->as<Literal>()->item().as<Numeric>()->round()->toInteger() == 1)
     {
         return makeGenericSequenceType(opType->itemType(),
                                        opCard.toWithoutMany());
     }
     else
     {
         return makeGenericSequenceType(opType->itemType(),
                                        opCard | Cardinality::zeroOrOne());
     }
 }

◆ typeCheck()

Expression::Ptr SubsequenceFN::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::FunctionCall.

Definition at line 220 of file qsequencefns.cpp.

 {
     m_hasTypeChecked = true;
     return FunctionCall::typeCheck(context, reqType);
 }

Properties

◆ m_hasTypeChecked

bool QPatternist::SubsequenceFN::m_hasTypeChecked

private

Definition at line 336 of file qsequencefns_p.h.

Referenced by staticType(), and typeCheck().

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

/src/xmlpatterns/functions/qsequencefns_p.h
/src/xmlpatterns/functions/qsequencefns.cpp

Public Functions

Properties

Additional Inherited Members

Detailed Description

Constructors and Destructors

◆ SubsequenceFN()

Functions

◆ compress()

◆ evaluateSequence()

◆ evaluateSingleton()

◆ staticType()

◆ typeCheck()

Properties

◆ m_hasTypeChecked