Qt 4.8
Public Functions | Private Functions | Static Private Functions | List of all members
QPatternist::CurrentItemStore Class Reference

Creates a DynamicContext which provides the focus item for the function fn:current(). More...

#include <qcurrentitemstore_p.h>

Inheritance diagram for QPatternist::CurrentItemStore:
QPatternist::SingleContainer QPatternist::Expression QSharedData QPatternist::CppCastingHelper< Expression > QPatternist::SourceLocationReflection

Public Functions

virtual ExpressionVisitorResult::Ptr accept (const ExpressionVisitor::Ptr &visitor) const
 
virtual const SourceLocationReflectionactualReflection () const
 Returns this. More...
 
virtual Expression::Ptr compress (const StaticContext::Ptr &context)
 
 CurrentItemStore (const Expression::Ptr &operand)
 
virtual bool evaluateEBV (const DynamicContext::Ptr &) const
 
virtual Item::Iterator::Ptr evaluateSequence (const DynamicContext::Ptr &) const
 
virtual Item evaluateSingleton (const DynamicContext::Ptr &) const
 
virtual SequenceType::List expectedOperandTypes () const
 
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::SingleContainer
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 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 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
 
virtual ID id () 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::Ptrrewrite (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 createContext (const DynamicContext::Ptr &old) const
 

Static Private Functions

static StaticContext::Ptr newStaticContext (const StaticContext::Ptr &context)
 

Additional Inherited Members

- Public Types inherited from QPatternist::Expression
typedef QExplicitlySharedDataPointer< const ExpressionConstPtr
 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::PtrList
 
typedef QFlags< PropertyProperties
 
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< ExpressionPtr
 A smart pointer wrapping mutable Expression instances. More...
 
typedef ::QAbstractXmlForwardIterator< Expression::PtrQAbstractXmlForwardIterator
 
typedef QVector< Expression::PtrVector
 
- 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::SingleContainer
 SingleContainer (const Expression::Ptr &operand)
 
- 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::SingleContainer
Expression::Ptr m_operand
 

Detailed Description

Creates a DynamicContext which provides the focus item for the function fn:current().

Author
Frans Englich frans.nosp@m..eng.nosp@m.lich@.nosp@m.noki.nosp@m.a.com
Since
4.5

Definition at line 71 of file qcurrentitemstore_p.h.

Constructors and Destructors

◆ CurrentItemStore()

CurrentItemStore::CurrentItemStore ( const Expression::Ptr operand)

Definition at line 53 of file qcurrentitemstore.cpp.

53  : SingleContainer(operand)
54 {
55 }
SingleContainer(const Expression::Ptr &operand)

Functions

◆ accept()

ExpressionVisitorResult::Ptr CurrentItemStore::accept ( const ExpressionVisitor::Ptr visitor) const
virtual

Implements QPatternist::Expression.

Definition at line 124 of file qcurrentitemstore.cpp.

125 {
126  return visitor->visit(this);
127 }

◆ actualReflection()

const SourceLocationReflection * CurrentItemStore::actualReflection ( ) const
virtual

Returns this.

Reimplemented from QPatternist::Expression.

Definition at line 129 of file qcurrentitemstore.cpp.

130 {
131  return m_operand->actualReflection();
132 }
virtual const SourceLocationReflection * actualReflection() const
Returns this.

◆ compress()

Expression::Ptr CurrentItemStore::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
contextthe 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 101 of file qcurrentitemstore.cpp.

102 {
104 
105  if(me != this)
106  return me;
107  else
108  {
109  /* If fn:current() isn't called, there's no point in us sticking
110  * around. */
112  return me;
113  else
114  return m_operand;
115  }
116 }
static StaticContext::Ptr newStaticContext(const StaticContext::Ptr &context)
bool testFlag(Enum f) const
Returns true if the flag is set, otherwise false.
Definition: qglobal.h:2345
virtual Expression::Ptr compress(const StaticContext::Ptr &context)
Properties deepProperties() const
Computes the union of properties for this Expression and all its descending children.

◆ createContext()

DynamicContext::Ptr CurrentItemStore::createContext ( const DynamicContext::Ptr old) const
inlineprivate

Definition at line 57 of file qcurrentitemstore.cpp.

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

58 {
59  return DynamicContext::Ptr(new CurrentItemContext(old->contextItem(), old));
60 }
virtual Item contextItem() const =0
A DynamicContext that maintains the focus, a sequence of items.
QExplicitlySharedDataPointer< DynamicContext > Ptr

◆ evaluateEBV()

bool CurrentItemStore::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 62 of file qcurrentitemstore.cpp.

63 {
64  return m_operand->evaluateEBV(createContext(context));
65 }
virtual bool evaluateEBV(const DynamicContext::Ptr &context) const
DynamicContext::Ptr createContext(const DynamicContext::Ptr &old) const

◆ evaluateSequence()

Item::Iterator::Ptr CurrentItemStore::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 qcurrentitemstore.cpp.

68 {
69  return m_operand->evaluateSequence(createContext(context));
70 }
DynamicContext::Ptr createContext(const DynamicContext::Ptr &old) const
virtual Item::Iterator::Ptr evaluateSequence(const DynamicContext::Ptr &context) const

◆ evaluateSingleton()

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

Reimplemented from QPatternist::Expression.

Definition at line 72 of file qcurrentitemstore.cpp.

73 {
74  return m_operand->evaluateSingleton(createContext(context));
75 }
DynamicContext::Ptr createContext(const DynamicContext::Ptr &old) const
virtual Item evaluateSingleton(const DynamicContext::Ptr &context) const

◆ expectedOperandTypes()

SequenceType::List CurrentItemStore::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 82 of file qcurrentitemstore.cpp.

83 {
84  SequenceType::List result;
86  return result;
87 }
static const SequenceType::Ptr ZeroOrMoreItems
void append(const T &t)
Inserts value at the end of the list.
Definition: qlist.h:507
The QList class is a template class that provides lists.
Definition: qdatastream.h:62

◆ newStaticContext()

StaticContext::Ptr CurrentItemStore::newStaticContext ( const StaticContext::Ptr context)
inlinestaticprivate

Definition at line 89 of file qcurrentitemstore.cpp.

Referenced by compress(), and typeCheck().

90 {
91  /* It might be we are generated despite there is no focus. In that case
92  * an error will reported in case current() is used, but in any case we cannot
93  * crash, so use item() in case we have no focus.
94  *
95  * Such a case is when we're inside a named template, and it's invoked
96  * without focus. */
97  const ItemType::Ptr t(context->contextItemType());
98  return StaticContext::Ptr(new StaticCurrentContext(t ? t : BuiltinTypes::item, context));
99 }
static const ItemType::Ptr item
A StaticContext that carries a specified static type for the current item, as returned by fn:current(...
virtual ItemType::Ptr contextItemType() const =0
The static type of the context item.
QExplicitlySharedDataPointer< StaticContext > Ptr

◆ properties()

Expression::Properties CurrentItemStore::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 134 of file qcurrentitemstore.cpp.

◆ staticType()

SequenceType::Ptr CurrentItemStore::staticType ( ) const
virtual
Returns
the staticType() of its operand.

Implements QPatternist::Expression.

Definition at line 77 of file qcurrentitemstore.cpp.

78 {
79  return m_operand->staticType();
80 }
virtual SequenceType::Ptr staticType() const =0

◆ typeCheck()

Expression::Ptr CurrentItemStore::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
contextsupplies 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.
reqTypethe 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 118 of file qcurrentitemstore.cpp.

120 {
121  return SingleContainer::typeCheck(newStaticContext(context), reqType);
122 }
static StaticContext::Ptr newStaticContext(const StaticContext::Ptr &context)
virtual Expression::Ptr typeCheck(const StaticContext::Ptr &context, const SequenceType::Ptr &reqType)
Definition: qexpression.cpp:70

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