Represents a let-clause, but is only used at compile time. More...

#include <qletclause_p.h>

Inheritance diagram for QPatternist::LetClause:

Public Functions
virtual ExpressionVisitorResult::Ptr	accept (const ExpressionVisitor::Ptr &visitor) const

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

	LetClause (const Expression::Ptr &operand1, const Expression::Ptr &operand2, const VariableDeclaration::Ptr &decl)

virtual 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::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 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 Functions
DynamicContext::Ptr	bindVariable (const DynamicContext::Ptr &context) const

Properties
const VariableDeclaration::Ptr	m_varDecl

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::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

Represents a let-clause, but is only used at compile time.

LetClause is inserted into the AST tree for the single purpose of ensuring that the focus is correct for the binding expression. Once that is done, LetClause sometimes rewrites itself to its return expression, and the ExpressionVariableReference will handle the evaluation of the variable.

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

Definition at line 78 of file qletclause_p.h.

Constructors and Destructors

◆ LetClause()

LetClause::LetClause	(	const Expression::Ptr &	operand1,
		const Expression::Ptr &	operand2,
		const VariableDeclaration::Ptr &	decl
	)

Definition at line 53 of file qletclause.cpp.

                                                          : PairContainer(operand1, operand2)
                                                            , m_varDecl(decl)
 {
     Q_ASSERT(m_varDecl);
 }

Functions

◆ accept()

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

virtual

Implements QPatternist::Expression.

Definition at line 132 of file qletclause.cpp.

 {
     return visitor->visit(this);
 }

◆ bindVariable()

DynamicContext::Ptr LetClause::bindVariable ( const DynamicContext::Ptr & context ) const

inlineprivate

Definition at line 61 of file qletclause.cpp.

Referenced by evaluateEBV(), evaluateSequence(), evaluateSingleton(), and evaluateToSequenceReceiver().

 {
     context->setExpressionVariable(m_varDecl->slot, m_operand1);
     return context;
 }

◆ evaluateEBV()

bool LetClause::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 77 of file qletclause.cpp.

 {
     return m_operand2->evaluateEBV(bindVariable(context));
 }

◆ evaluateSequence()

Item::Iterator::Ptr LetClause::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 67 of file qletclause.cpp.

 {
     return m_operand2->evaluateSequence(bindVariable(context));
 }

◆ evaluateSingleton()

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

virtual

Reimplemented from QPatternist::Expression.

Definition at line 72 of file qletclause.cpp.

 {
     return m_operand2->evaluateSingleton(bindVariable(context));
 }

◆ evaluateToSequenceReceiver()

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

virtual

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

Reimplemented from QPatternist::Expression.

Definition at line 82 of file qletclause.cpp.

 {
     m_operand2->evaluateToSequenceReceiver(bindVariable(context));
 }

◆ expectedOperandTypes()

SequenceType::List LetClause::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 119 of file qletclause.cpp.

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

◆ id()

Expression::ID LetClause::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 137 of file qletclause.cpp.

 {
     return IDLetClause;
 }

◆ properties()

Expression::Properties LetClause::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 114 of file qletclause.cpp.

 {
     return m_varDecl->expression()->properties() & (Expression::RequiresFocus | Expression::IsEvaluated | Expression::DisableElimination);
 }

◆ staticType()

SequenceType::Ptr LetClause::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 127 of file qletclause.cpp.

 {
     return m_operand2->staticType();
 }

◆ typeCheck()

Expression::Ptr LetClause::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 87 of file qletclause.cpp.

 {
     /* Consider the following query:
      *
      * <tt>let $d := <child type=""/>
      * return $d//\*[let $i := @type
      *              return $d//\*[$i]]</tt>
      *
      * The node test <tt>@type</tt> is referenced from two different places,
      * where each reference have a different focus. So, in the case of that the source
      * uses the focus, we need to use a DynamicContextStore to ensure the variable
      * is always evaluated with the correct focus, regardless of where it is referenced
      * from.
      *
      * We miss out a lot of false positives. For instance, the case of where the focus
      * is identical for everyone. One reason we cannot check this, is that Expression
      * doesn't know about its parent.
      */
     m_varDecl->canSourceRewrite = !m_operand1->deepProperties().testFlag(RequiresFocus);
 
     if(m_varDecl->canSourceRewrite)
         return m_operand2->typeCheck(context, reqType);
     else
         return PairContainer::typeCheck(context, reqType);
 }

Properties

◆ m_varDecl

const VariableDeclaration::Ptr QPatternist::LetClause::m_varDecl

private

Definition at line 101 of file qletclause_p.h.

Referenced by bindVariable(), LetClause(), properties(), and typeCheck().

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

/src/xmlpatterns/expr/qletclause_p.h
/src/xmlpatterns/expr/qletclause.cpp

Public Functions

Private Functions

Properties

Additional Inherited Members

Detailed Description

Constructors and Destructors

◆ LetClause()

Functions

◆ accept()

◆ bindVariable()

◆ evaluateEBV()

◆ evaluateSequence()

◆ evaluateSingleton()

◆ evaluateToSequenceReceiver()

◆ expectedOperandTypes()

◆ id()

◆ properties()

◆ staticType()

◆ typeCheck()

Properties

◆ m_varDecl