Implements XPath 2.0's conditional expression if([expr]) then [expr] else [expr]. More...

#include <qifthenclause_p.h>

Inheritance diagram for QPatternist::IfThenClause:

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

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

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

virtual SequenceType::List	expectedOperandTypes () const

virtual ID	id () const

	IfThenClause (const Expression::Ptr &test, const Expression::Ptr &then, const Expression::Ptr &el)

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

virtual SequenceType::Ptr	staticType () const

Public Functions inherited from QPatternist::TripleContainer
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 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 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::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 ()

Additional Inherited Members
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::TripleContainer
	TripleContainer (const Expression::Ptr &operand1, const Expression::Ptr &operand2, const Expression::Ptr &operand3)

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::TripleContainer
Expression::Ptr	m_operand1

Expression::Ptr	m_operand2

Expression::Ptr	m_operand3

Detailed Description

Implements XPath 2.0's conditional expression if([expr]) then [expr] else [expr].

See also: XML Path Language (XPath) 2.0, 3.8 Conditional Expressions

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

Definition at line 71 of file qifthenclause_p.h.

Constructors and Destructors

◆ IfThenClause()

IfThenClause::IfThenClause	(	const Expression::Ptr &	test,
		const Expression::Ptr &	then,
		const Expression::Ptr &	el
	)

Definition at line 52 of file qifthenclause.cpp.

                                                     : TripleContainer(test, then, el)
 {
 }

Functions

◆ accept()

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

virtual

Implements QPatternist::Expression.

Definition at line 131 of file qifthenclause.cpp.

 {
     return visitor->visit(this);
 }

◆ compress()

Expression::Ptr IfThenClause::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 87 of file qifthenclause.cpp.

 {
     const Expression::Ptr me(TripleContainer::compress(context));
 
     if(me != this)
         return me;
 
     /* All operands mustn't be evaluated in order for const folding to
      * be possible. Let's see how far we get. */
 
     if(m_operand1->isEvaluated())
     {
         if(m_operand1->evaluateEBV(context->dynamicContext()))
             return m_operand2;
         else
             return m_operand3;
     }
     else
         return me;
 }

◆ evaluateEBV()

bool IfThenClause::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 72 of file qifthenclause.cpp.

 {
     return m_operand1->evaluateEBV(context)
             ? m_operand2->evaluateEBV(context)
             : m_operand3->evaluateEBV(context);
 }

◆ evaluateSequence()

Item::Iterator::Ptr IfThenClause::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 58 of file qifthenclause.cpp.

 {
     return m_operand1->evaluateEBV(context)
             ? m_operand2->evaluateSequence(context)
             : m_operand3->evaluateSequence(context);
 }

◆ evaluateSingleton()

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

virtual

Reimplemented from QPatternist::Expression.

Definition at line 65 of file qifthenclause.cpp.

 {
     return m_operand1->evaluateEBV(context)
             ? m_operand2->evaluateSingleton(context)
             : m_operand3->evaluateSingleton(context);
 }

◆ evaluateToSequenceReceiver()

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

virtual

Evaluates this Expression by sending its output to DynamicContext::outputReceiver().

Reimplemented from QPatternist::Expression.

Definition at line 79 of file qifthenclause.cpp.

 {
     if(m_operand1->evaluateEBV(context))
         m_operand2->evaluateToSequenceReceiver(context);
     else
         m_operand3->evaluateToSequenceReceiver(context);
 }

◆ expectedOperandTypes()

SequenceType::List IfThenClause::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 113 of file qifthenclause.cpp.

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

◆ id()

Expression::ID IfThenClause::id ( ) const

virtual

Returns: IDIfThenClause

Reimplemented from QPatternist::Expression.

Definition at line 136 of file qifthenclause.cpp.

 {
     return IDIfThenClause;
 }

◆ optimizationPasses()

QList< QExplicitlySharedDataPointer< OptimizationPass > > IfThenClause::optimizationPasses ( ) const

virtual

Returns the OptimizationPasses that applies for this Expression. The default implementation returns an empty list. Sub-classes can re-implement this function and return actual OptimizationPasses.

Returns: always an empty list.

Reimplemented from QPatternist::Expression.

Definition at line 108 of file qifthenclause.cpp.

 {
     return OptimizationPasses::ifThenPasses;
 }

◆ staticType()

SequenceType::Ptr IfThenClause::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 122 of file qifthenclause.cpp.

 {
     const SequenceType::Ptr t1(m_operand2->staticType());
     const SequenceType::Ptr t2(m_operand3->staticType());
 
     return makeGenericSequenceType(t1->itemType() | t2->itemType(),
                                    t1->cardinality() | t2->cardinality());
 }

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

/src/xmlpatterns/expr/qifthenclause_p.h
/src/xmlpatterns/expr/qifthenclause.cpp

Public Functions

Additional Inherited Members

Detailed Description

Constructors and Destructors

◆ IfThenClause()

Functions

◆ accept()

◆ compress()

◆ evaluateEBV()

◆ evaluateSequence()

◆ evaluateSingleton()

◆ evaluateToSequenceReceiver()

◆ expectedOperandTypes()

◆ id()

◆ optimizationPasses()

◆ staticType()