Implements the path expression, containing two steps, such as in html/body. More...

#include <qpath_p.h>

Inheritance diagram for QPatternist::Path:

Public Types
enum	Kind { RegularPath = 1, XSLTForEach, ForApplyTemplate }

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

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

virtual SequenceType::List	expectedOperandTypes () const

virtual ID	id () const

Kind	kind () const

Item::Iterator::Ptr	mapToSequence (const Item &item, const DynamicContext::Ptr &context) const

virtual ItemType::Ptr	newFocusType () const

	Path (const Expression::Ptr &operand1, const Expression::Ptr &operand2, const Kind kind=RegularPath)

virtual Properties	properties () const

void	setLast ()

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)

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 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 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 Path >	ConstPtr

Properties
bool	m_checkXPTY0018

bool	m_hasCreatedSorter

bool	m_isLast

const Kind	m_kind

Additional Inherited Members
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::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 the path expression, containing two steps, such as in html/body.

See also: XQuery 1.0: An XML Query Language, 3.2 Path Expressions

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

Definition at line 72 of file qpath_p.h.

Typedefs

◆ ConstPtr

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

private

Definition at line 140 of file qpath_p.h.

Enumerations

◆ Kind

enum QPatternist::Path::Kind

Enumerator
RegularPath	This Path is a plain old path expression as found in XPath. Sorting is performed, and atomics are disallowed as left operand.
XSLTForEach	This Path emulates an `xsl:for-each` instruction. This means no sorting of result, and atomics are allowed as left operand.
ForApplyTemplate	This Path performs the iteration in an `xsl:apply-templates` instruction. This means sorting, and atomics are disallowed as left operand.

Definition at line 75 of file qpath_p.h.

         {
             RegularPath = 1,
 
             XSLTForEach,
 
             ForApplyTemplate
         };

Constructors and Destructors

◆ Path()

Path::Path	(	const Expression::Ptr &	operand1,
		const Expression::Ptr &	operand2,
		const Kind	kind = `RegularPath`
	)

Definition at line 56 of file qpath.cpp.

                             : PairContainer(operand1, operand2)
                             , m_hasCreatedSorter(kind != RegularPath)
                             , m_isLast(false)
                             , m_checkXPTY0018(kind == RegularPath)
                             , m_kind(kind)
 {
 }

Functions

◆ accept()

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

virtual

Implements QPatternist::Expression.

Definition at line 251 of file qpath.cpp.

 {
     return visitor->visit(this);
 }

◆ compress()

Expression::Ptr Path::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 162 of file qpath.cpp.

 {
     const Expression::Ptr me(PairContainer::compress(context));
 
     /* "./expr" is by now equal to "expr" since we've done
      * focus/type checks, and a node sorter has been inserted. */
     if(m_operand1->is(IDContextItem))
         return m_operand2;
 
     /* We do this as late as we can, such that we pick up the most recent type
      * from the operand. */
     if(m_isLast && m_kind != XSLTForEach && m_operand2->staticType()->itemType() == BuiltinTypes::item)
         m_checkXPTY0018 = true;
 
     return me;
 }

◆ evaluateSequence()

Item::Iterator::Ptr Path::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 77 of file qpath.cpp.

 {
     /* Note, we use the old context for m_operand1. */
     const Item::Iterator::Ptr source(m_operand1->evaluateSequence(context));
 
     const DynamicContext::Ptr focus(context->createFocus());
     focus->setFocusIterator(source);
 
     const Item::Iterator::Ptr result(makeSequenceMappingIterator<Item>(ConstPtr(this), source, focus));
 
     if(m_checkXPTY0018)
     {
         /* This is an expensive code path, but it should happen very rarely. */
 
         enum FoundItem
         {
             FoundNone,
             FoundNode,
             FoundAtomicValue
         } hasFound = FoundNone;
 
         Item::List whenChecked;
 
         Item next(result->next());
 
         while(next)
         {
             const FoundItem found = next.isAtomicValue() ? FoundAtomicValue : FoundNode;
 
             if(hasFound != FoundNone && hasFound != found)
             {
                 /* It's an atomic value and we've already found a node. Mixed content. */
                 context->error(QtXmlPatterns::tr("The last step in a path must contain either nodes "
                                                  "or atomic values. It cannot be a mixture between the two."),
                                ReportContext::XPTY0018, this);
             }
             else
                 hasFound = found;
 
             whenChecked.append(next);
             next = result->next();
         }
 
         return makeListIterator(whenChecked);
     }
     else
         return result;
 }

◆ evaluateSingleton()

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

virtual

Reimplemented from QPatternist::Expression.

Definition at line 126 of file qpath.cpp.

 {
     /* This function is called if both operands' cardinality is exactly-one. Therefore
      * we manually go forward in the focus by calling next().
      *
      * We don't check for XPTY0018, only in evaluateSequence(), since if we're guaranteed
      * to evaluate to one item, we can only evaluate to one node or one atomic value.
      */
 
     /* Note, we use the old context for m_operand1. */
     const Item::Iterator::Ptr source(m_operand1->evaluateSequence(context));
 
     const DynamicContext::Ptr focus(context->createFocus());
     focus->setFocusIterator(source);
 
     /* This test is needed because if the focus is empty, we don't want to(nor can't) evaluate
      * the next step. */
     // TODO Why are we at all invoked then?
     if(source->next())
         return m_operand2->evaluateSingleton(focus);
     else
         return Item();
 }

◆ evaluateToSequenceReceiver()

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

virtual

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

Reimplemented from QPatternist::Expression.

Definition at line 150 of file qpath.cpp.

 {
     /* Note, we use the old context for m_operand1. */
     const Item::Iterator::Ptr source(m_operand1->evaluateSequence(context));
 
     const DynamicContext::Ptr focus(context->createFocus());
     focus->setFocusIterator(source);
 
     while(source->next())
         m_operand2->evaluateToSequenceReceiver(focus);
 }

◆ expectedOperandTypes()

SequenceType::List Path::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 223 of file qpath.cpp.

 {
     SequenceType::List result;
 
     /* This value needs to be in sync with what we pass to
      * applyFunctionConversion() in typeCheck() above.
      *
      * We don't have the XPTY0019 restriction when we're synthetic XSL-T code.
      */
     if(m_kind == XSLTForEach)
         result.append(CommonSequenceTypes::ZeroOrMoreItems);
     else
         result.append(CommonSequenceTypes::ZeroOrMoreNodes);
 
     result.append(CommonSequenceTypes::ZeroOrMoreItems);
     return result;
 }

◆ id()

Expression::ID Path::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 266 of file qpath.cpp.

 {
     return IDPath;
 }

◆ kind()

Kind QPatternist::Path::kind ( ) const

inline

Definition at line 134 of file qpath_p.h.

         {
             return m_kind;
         }

◆ mapToSequence()

Item::Iterator::Ptr Path::mapToSequence	(	const Item &	item,
		const DynamicContext::Ptr &	context
	)		const

inline

Definition at line 66 of file qpath.cpp.

 {
     /* item is the focus here. That is in <e/>/1, item is <e/>. However,
      * we don't use it, since the context item is accessed through
      * DynamicContext::focusIterator() and friends. */
     Q_ASSERT(item);
     Q_UNUSED(item); /* Needed when compiling in release mode. */
     return m_operand2->evaluateSequence(context);
 }

◆ newFocusType()

ItemType::Ptr Path::newFocusType ( ) const

virtual

Returns: the item type of the last step's static type.

Reimplemented from QPatternist::Expression.

Definition at line 261 of file qpath.cpp.

Referenced by typeCheck().

 {
     return m_operand1->staticType()->itemType();
 }

◆ properties()

Expression::Properties Path::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 256 of file qpath.cpp.

 {
     return CreatesFocusForLast | ((m_operand1->properties() | m_operand2->properties()) & (RequiresCurrentItem | DisableElimination));
 }

◆ setLast()

void Path::setLast ( )

inline

Definition at line 166 of file qpath_p.h.

     {
         m_isLast = true;
     }

◆ staticType()

SequenceType::Ptr Path::staticType ( ) const

virtual

Returns: the static type of the last step where the cardinality is multiplied with the cardinality of the first step's cardinality.

Implements QPatternist::Expression.

Definition at line 241 of file qpath.cpp.

 {
     const SequenceType::Ptr opType(m_operand2->staticType());
 
     /* For each parent step, we evaluate the child step. So multiply the two
      * cardinalities. */
     return makeGenericSequenceType(opType->itemType(),
                                    m_operand1->staticType()->cardinality() * opType->cardinality());
 }

◆ typeCheck()

Expression::Ptr Path::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 179 of file qpath.cpp.

 {
     m_operand2->announceFocusType(newFocusType());
 
     /* Here we apply the function conversion first, and with the error code
      * that we want -- XPTY0019 instead of XPTY0004. Unfortunately
      * PairContainer::typeCheck() will do the type check again, which is
      * redundant in the case of when we're not XSLTForEach.
      *
      * If we're XSLTForEach, it means we're a synthetic "map" expression for
      * implementing various XSL-T expressions, and hence don't have the
      * constraint of XPTY0019.
      *
      * It's important that typeCheck() is run for the operands(of course), and the call to
      * PairContainer::typeCheck() ensures that below, in the case that we're XSL-T code.
      *
      * The type we expect, CommonSequenceTypes::ZeroOrMoreNodes() needs to be in sync with
      * what we return in expectedOperandTypes(). */
     if(m_kind != XSLTForEach)
     {
         m_operand1 = TypeChecker::applyFunctionConversion(m_operand1,
                                                           CommonSequenceTypes::ZeroOrMoreNodes,
                                                           context,
                                                           m_kind == ForApplyTemplate ? ReportContext::XTTE0520
                                                                                      : ReportContext::XPTY0019);
     }
 
     /* If our step ends with atomic values, we cannot sort.
      *
      * We must smack the NodeSortExpression ontop before calling typeCheck(), since the latter
      * may insert an Atomizer, as possibly mandated by reqType. By doing it after, the Atomizer
      * will be a parent to NodeSortExpression, as opposed to a child.
      */
     if(!m_hasCreatedSorter)
     {
         m_hasCreatedSorter = true;
 
         return NodeSortExpression::wrapAround(Expression::Ptr(this), context)->typeCheck(context, reqType);
     }
     else
         return PairContainer::typeCheck(context, reqType);
 }

Properties

◆ m_checkXPTY0018

bool QPatternist::Path::m_checkXPTY0018

private

Definition at line 162 of file qpath_p.h.

Referenced by compress(), and evaluateSequence().

◆ m_hasCreatedSorter

bool QPatternist::Path::m_hasCreatedSorter

private

One might think this block exists for preventing multiple NodeSortExpressions to be created. However, that is not an issue, since NodeSortExpression optimizes this away anyway.

The real reason is to avoid infinite recursion. When our typeCheck() forwards on the type check to the just created NodeSortExpression, it in turn calls typeCheck() on its child, which is this Path. Rince and repeat.

We only create node sorts when we're a regular path expression, and not when standing in as a generic map expression.

Definition at line 154 of file qpath_p.h.

Referenced by typeCheck().

◆ m_isLast

bool QPatternist::Path::m_isLast

private

Whether this path is the step. For instance, in a/b/c, the last path has c as the right operand.

Definition at line 160 of file qpath_p.h.

Referenced by compress(), and setLast().

◆ m_kind

const Kind QPatternist::Path::m_kind

private

Definition at line 163 of file qpath_p.h.

Referenced by compress(), expectedOperandTypes(), kind(), and typeCheck().

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

/src/xmlpatterns/expr/qpath_p.h
/src/xmlpatterns/expr/qpath.cpp

Public Types

Public Functions

Private Types

Properties

Additional Inherited Members

Detailed Description

Typedefs

◆ ConstPtr

Enumerations

◆ Kind

Constructors and Destructors

◆ Path()

Functions

◆ accept()

◆ compress()

◆ evaluateSequence()

◆ evaluateSingleton()

◆ evaluateToSequenceReceiver()

◆ expectedOperandTypes()

◆ id()

◆ kind()

◆ mapToSequence()

◆ newFocusType()

◆ properties()

◆ setLast()

◆ staticType()

◆ typeCheck()

Properties

◆ m_checkXPTY0018

◆ m_hasCreatedSorter

◆ m_isLast

◆ m_kind