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+/****************************************************************************
+**
+** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
+** All rights reserved.
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the QtXmlPatterns module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** No Commercial Usage
+** This file contains pre-release code and may not be distributed.
+** You may use this file in accordance with the terms and conditions
+** contained in the Technology Preview License Agreement accompanying
+** this package.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Nokia gives you certain additional
+** rights.  These rights are described in the Nokia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** If you have questions regarding the use of this file, please contact
+** Nokia at qt-info@nokia.com.
+**
+**
+**
+**
+**
+**
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists purely as an
+// implementation detail.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+#ifndef Patternist_Expression_H
+#define Patternist_Expression_H
+#include <QFlags>
+#include <QSharedData>
+#include "qcppcastinghelper_p.h"
+#include "qdebug_p.h"
+#include "qdynamiccontext_p.h"
+#include "qexpressiondispatch_p.h"
+#include "qitem_p.h"
+#include "qsequencetype_p.h"
+#include "qsourcelocationreflection_p.h"
+#include "qstaticcontext_p.h"
+QT_BEGIN_HEADER
+QT_BEGIN_NAMESPACE
+template<typename T> class QList;
+template<typename T> class QVector;
+namespace QPatternist
+{
+template<typename T, typename ListType> class ListIterator;
+class OptimizationPass;
+/**
+* @short Base class for all AST nodes in an XPath/XQuery/XSL-T expression.
+*
+* @section ExpressionCreation Expression Compilation
+*
+* @subsection ExpressionCreationParser The process of creating an Expression
+*
+* The initial step of creating an internal representation(in some circles
+* called an IR tree) of the XPath string follows classic compiler design: a scanner
+* is invoked, resulting in tokens, which sub-sequently are consumed by a parser
+* which groups the tokens into rules, resulting in the creation of
+* Abstract Syntax Tree(AST) nodes that are arranged in a hierarchical structure
+* similar to the EBNF.
+*
+* More specifically, ExpressionFactory::createExpression() is called with a
+* pointer to a static context, and the string for the expression. This is subsequently
+* tokenized by a Flex scanner. Mistakes detected at this stage is syntax
+* errors, as well as a few semantical errors. Syntax errors can be divided
+* in two types:
+*
+*     - The scanner detects it. An example is the expression "23Eb3" which
+*     is not a valid number literal, or "1prefix:my-element" which is not a
+*     valid QName.
+*     - The parser detects it. This means a syntax error at a
+*     higher level, that a group of tokens couldn't be reduced to a
+*     rule(expression). An example is the expression "if(a = b) 'match' else
+*     'no match'"; the tokenizer would handle it fine, but the parser would
+*     fail because the tokens could not be reduced to a rule due to the token
+*     for the "then" word was missing.
+*
+* Apart from the syntax errors, the actions in the parser also detects
+* errors when creating the corresponding expressions. This is for example
+* that no namespace binding for a prefix could be found, or that a function
+* call was used which no function implementation could be found for.
+*
+* When the parser has finished, the result is an AST. That is, a
+* hierarchical structure consisting of Expression sub-classes. The
+* individual expressions haven't at this point done anything beyond
+* receiving their child-expressions(if any), and hence reminds of a
+* "construction scaffold". In other words, a tree for the expression
+* <tt>'string' + 1 and xs:date('2001-03-13')</tt> could have been created, even if
+* that expression contains errors(one can't add a xs:integer to a xs:string,
+* and the Effective %Boolean Value cannot be extracted for date types).
+*
+* @subsection ExpressionCreationTypeChecking Type Checking
+*
+* After the AST creation, ExpressionFactory::createExpression continues with
+* calling the AST node(which is an Expression instance)'s typeCheck()
+* function. This step ensures that the static types of the operands matches
+* the operators, and in the cases where it doesn't, modifies the AST such
+* that the necessary conversions are done -- if possible, otherwise the
+* result is a type error.
+*
+*
+* This step corresponds roughly to what <a
+* href="http://www.w3.org/TR/xpath20/#id-static-analysis">2.2.3.1 Static Analysis Phase</a>
+* labels operation tree normalization; step SQ5.
+*
+* @subsection ExpressionCreationCompression Compressing -- Optimization and Fixup
+*
+* The last step is calling compress(). This function is not called
+* 'optimize', 'simplify' or the like, because although it performs all
+* optimization, it also involves mandatory stages.
+*
+* One such is const folding, which while being an efficient optimization,
+* also is a necessity for many XSL-T constructs. Another important step is
+* that functions which had an evaluation dependency on the static context(as
+* opposed to the dynamic) performs their "fixup".
+*
+* In other words, this stage potentially performs AST re-writes. For example,
+* the expression <tt>3 + 3, concat('foo', '-', 'bar'), true() and false()</tt> would
+* result in an AST corresponding to <tt>6, 'foo-bar', false()</tt>. This process
+* is done backwards; each expression asks its operands to compress before it
+* performs its own compression(and so forth, until the root expression's call
+* returns to the caller).
+*
+* @see <a href="http://www.w3.org/TR/xpath20/#id-errors-and-opt">XML Path Language
+* (XPath) 2.0, 2.3.4 Errors and Optimization</a>
+* @see <a href="http://www.w3.org/TR/xpath20/#id-expression-processing">XML Path
+* Language (XPath) 2.0, 2.2.3 Expression Processing</a>
+* @see <a href="http://www.w3.org/TR/xquery-xpath-parsing/">Building a Tokenizer
+* for XPath or XQuery</a>
+* @see ExpressionFactory
+* @author Frans Englich <frans.englich@nokia.com>
+* @ingroup Patternist_expressions
+*/
+class Q_AUTOTEST_EXPORT Expression : public QSharedData
+, public CppCastingHelper<Expression>
+, public SourceLocationReflection
+{
+public:
+/**
+* @short A smart pointer wrapping mutable Expression instances.
+*/
+typedef QExplicitlySharedDataPointer<Expression> Ptr;
+/**
+* @short A smart pointer wrapping @c const Expression instances.
+*/
+typedef QExplicitlySharedDataPointer<const Expression> ConstPtr;
+/**
+* A list of Expression instances, each wrapped in a smart pointer.
+*/
+typedef QList<Expression::Ptr> List;
+/**
+* A vector of Expression instances, each wrapped in a smart pointer.
+*/
+typedef QVector<Expression::Ptr> Vector;
+typedef QT_PREPEND_NAMESPACE(QAbstractXmlForwardIterator<Expression::Ptr>)
+QAbstractXmlForwardIterator;
+/**
+* Enum flags describing the characteristics of the expression.
+*
+* @see Expression::properties()
+*/
+enum Property
+{
+/**
+* This flag applies for functions, and results in the expression <tt>.</tt>
+* being appended to its operands if its operand count is lower than the
+* maximum amount of arguments.
+*
+* In effect, it result in a modification of the function's arguments to have
+* appended the context item.
+*
+* One function which has this property is <tt>fn:number()</tt>.
+*
+* @see ContextItem
+* @see <a href="http://www.w3.org/TR/xpath-functions/#func-signatures">XQuery 1.0 and
+* XPath 2.0 Functions and Operators, 1.3 Function Signatures and Descriptions</a>
+*/
+UseContextItem              = 1,
+/**
+* Disables compression(evaluation at compile time), such that the
+* Expression isn't const-folded, but ensured to be run at runtime. The
+* operands are still attempted to be compressed, unless
+* they override compression as well.
+*
+* @see compress()
+*/
+DisableElimination          = 1 << 1,
+/**
+* Signals that the expression is already evaluated and can be considered
+* a constant value.
+* For example, atomic values return this flag in their
+* implementations of the properties() functions.
+*
+* @see isEvaluated()
+*/
+IsEvaluated                 = 1 << 2,
+/**
+* Signals that the expression cannot be optimized away by judging
+* its static type.
+*
+* This is currently used for properly handling the @c none type, in
+* the <tt>fn:error()</tt> function. In type operations, the none type doesn't show
+* up and that can make expressions, such as InstanceOf, believe
+* it is safe to const fold, while it in fact is not.
+*/
+DisableTypingDeduction      = 1 << 3,
+/**
+* This property affects the static type -- staticType() -- of an expression. It
+* is implemented in FunctionCall::staticType() and therefore only work for FunctionCall
+* sub-classes and when that function is not re-implemented in an inhibiting way.
+*
+* When set, the cardinality of the static type is zero if the Expression's first
+* operand allows an empty sequence, otherwise it is the cardinality of the Expression's
+* static type modulo Cardinality::empty(). This is used for specifying proper static
+* type inference for functions that have "If $arg is the empty sequence,
+* the empty sequence is returned." However, before setting this property one
+* must be aware that no other conditions can lead to the empty sequence, since
+* otherwise the static type would be wrong.
+*/
+EmptynessFollowsChild       = 1 << 4,
+/**
+* This is similar to EmptynessFollowsChild, and also implemented in FunctionCall.
+* When set, it makes FunctionCall::typeCheck() rewrite itself into an empty sequence
+* if the first operand is the empty sequence.
+*
+* This property is often used together with EmptynessFollowsChild.
+*/
+RewriteToEmptyOnEmpty       = 1 << 5,
+/**
+* When set, it signals that the focus cannot be undefined. For example,
+* the <tt>fn:position()</tt> function extracts information from the focus. Setting
+* this flag ensures type checking is carried out appropriately.
+*
+* However, setting RequiresFocus does not imply this Expression requires the context
+* item to be defined. It only means the focus, of somekind, needs to be defined.
+*
+* @see RequiresContextItem
+*/
+RequiresFocus               = 1 << 6,
+/**
+* An Expression with this Property set, signals that it only affects
+* the order of its return value.
+*/
+AffectsOrderOnly            = 1 << 7,
+/**
+* When set, signals that the context item, must be defined for this Expression. When
+* setting this property, expectedContextItemType() must be re-implemented.
+*
+* Setting this property also sets RequiresFocus.
+*
+* @see DynamicContext::contextItem()
+*/
+RequiresContextItem         = (1 << 8) | RequiresFocus,
+/**
+* When set, signals that this expression creates a focus for its last operand.
+* When set, newFocusType() must be overridden to return the static type
+* of the context item.
+*
+* @see announceFocusType()
+* @see newFocusType()
+*/
+CreatesFocusForLast         = 1 << 9,
+/**
+* Signals that the last operand is a collation argument. This ensures
+* that the necessary code is generated for checking that the collation
+* is supported.
+*
+* This only applies to sub-classes of FunctionCall.
+*/
+LastOperandIsCollation      = 1 << 10,
+/**
+* When set, the Expression depends on local variables such as
+* those found in @c for expressions. However, this does not
+* include let bindings.
+*/
+DependsOnLocalVariable      = (1 << 11) | DisableElimination,
+/**
+* When set, it signals that the Expression does not need
+* an evaluation cache, despite what other flags might imply.
+*/
+EvaluationCacheRedundant       = (1 << 12),
+/**
+* Signals that the Expression constructs nodes, either directly
+* or computationally. For example, AttributeConstructor has this property
+* set.
+*
+* Since node constructors constructs nodes which have node
+* identities, node constructors are considered creative on
+* evaluation.
+*/
+IsNodeConstructor           = 1 << 13,
+/**
+* Whether this expression requires the current item, as returned
+* from @c fn:current().
+*
+* CurrentFN uses this flag.
+*/
+RequiresCurrentItem         = 1 << 14
+};
+/**
+* A QFlags template for type-safe handling of ExpressionProperty values. If
+* Expression::Property flags needs to be stored in a class, declared the variable
+* to be of type Expression::Properties.
+*
+* @see QFlags
+*/
+typedef QFlags<Property> Properties;
+/**
+* Enumerators that identifies Expression sub-classes.
+*
+* @see id()
+*/
+enum ID
+{
+/**
+* Identifies Boolean.
+*/
+IDBooleanValue = 1,
+/**
+* Identifies CountFN.
+*/
+IDCountFN,
+/**
+* Identifies EmptyFN.
+*/
+IDEmptyFN,
+/**
+* Identifies ExistsFN.
+*/
+IDExistsFN,
+/**
+* Identifies ExpressionSequence and LiteralSequence.
+*/
+IDExpressionSequence,
+/**
+* Identifies GeneralComparison.
+*/
+IDGeneralComparison,
+/**
+* Identifies IfThenClause.
+*/
+IDIfThenClause,
+/**
+* Identifies nothing in particular. The default implementation
+* of id() returns this, which is suitable for Expression instances
+* which never needs to be identified in this aspect.
+*/
+IDIgnorableExpression,
+/**
+* Identifies Integer.
+*/
+IDIntegerValue,
+/**
+* Identifies PositionFN.
+*/
+IDPositionFN,
+/**
+* Identifies AtomicString, AnyURI, and UntypedAtomic.
+*/
+IDStringValue,
+/**
+* Identifies ValueComparison.
+*/
+IDValueComparison,
+/**
+* Identifies VariableReference.
+*/
+IDRangeVariableReference,
+/**
+* Identifies ContextItem.
+*/
+IDContextItem,
+/**
+* Identifies UserFunctionCallsite.
+*/
+IDUserFunctionCallsite,
+/**
+* Identifies ExpressionVariableReference.
+*/
+IDExpressionVariableReference,
+/**
+* Identifies ExpressionVariableReference.
+*/
+IDAttributeConstructor,
+/**
+* Identifies UpperCaseFN.
+*/
+IDUpperCaseFN,
+/**
+* Identifies LowerCaseFN.
+*/
+IDLowerCaseFN,
+/**
+* Identifies FirstItemPredicate.
+*/
+IDFirstItemPredicate,
+IDEmptySequence,
+IDReturnOrderBy,
+IDLetClause,
+IDForClause,
+IDPath,
+IDNamespaceConstructor,
+IDArgumentReference,
+IDGenericPredicate,
+IDAxisStep,
+/**
+* A literal which is either @c xs:float or
+* @c xs:double.
+*/
+IDFloat,
+IDCombineNodes,
+IDUnresolvedVariableReference,
+IDCardinalityVerifier
+};
+inline Expression()
+{
+}
+virtual ~Expression();
+/**
+* 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.
+*/
+virtual Item::Iterator::Ptr evaluateSequence(const DynamicContext::Ptr &context) const;
+/**
+* @todo Docs
+*/
+virtual Item evaluateSingleton(const DynamicContext::Ptr &context) const;
+/**
+* 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 <a href="http://www.w3.org/TR/xpath20/#id-ebv">XML Path Language (XPath) 2.0,
+* 2.4.3 Effective Boolean Value</a>
+*/
+virtual bool evaluateEBV(const DynamicContext::Ptr &context) const;
+/**
+* Evaluates this Expression by sending its output to DynamicContext::outputReceiver().
+*/
+virtual void evaluateToSequenceReceiver(const DynamicContext::Ptr &context) const;
+/**
+* @returns the expression's child expressions. For example, a function's
+* arguments is returned here.
+*
+* If this Expression has no operands, an empty list should be returned.
+*/
+virtual Expression::List operands() const = 0;
+virtual void setOperands(const Expression::List &operands) = 0;
+/**
+* @returns the static type of this Expression. For example, an 'and' expression
+* have as static type xs:boolean
+*/
+virtual SequenceType::Ptr staticType() const = 0;
+/**
+* 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.
+*/
+virtual SequenceType::List expectedOperandTypes() const = 0;
+/**
+* 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.
+*
+* @param context supplies information, such as namespace bindings and
+* available function signatures, that can be needed at compilation time. @p context is
+* guaranteed by the caller to never null.
+* @param reqType the static type that this Expression must match when evaluated. @p 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
+* @p reqType
+*/
+virtual Expression::Ptr typeCheck(const StaticContext::Ptr &context,
+const SequenceType::Ptr &reqType);
+/**
+* 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().
+*
+* @param context the static context. Supplies compile time information, and is
+* the channel for communicating error messages.
+* @see <a href="http://en.wikipedia.org/wiki/Sparse_conditional_constant_propagation">Wikipedia,
+* the free encyclopedia, Sparse conditional constant propagation</a>
+* @see <a href="http://en.wikipedia.org/wiki/Intrinsic_function">Wikipedia,
+* the free encyclopedia, Intrinsic function</a>
+* @see <a href="http://en.wikipedia.org/wiki/Compiler_optimization">Wikipedia, the
+* free encyclopedia, Compiler optimization</a>
+*/
+virtual Expression::Ptr compress(const StaticContext::Ptr &context);
+/**
+* @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 deepProperties()
+* @returns Expression::None, meaning no special properties
+*/
+virtual Properties properties() const;
+/**
+* Recursively computes through all descendants until a Property
+* is encount
+*/
+virtual Properties dependencies() const;
+/**
+* @short Computes the union of properties for this Expression and all
+* its descending children.
+*
+* @see properties()
+*/
+Properties deepProperties() const;
+/**
+* This function is a utility function, which performs bitwise logic
+* on properties() in order to find out whether the Expression::IsEvaluated
+* flag is set.
+*
+* @note Do not attempt to re-implement this function. Instead, return the
+* IsEvaluated flag by re-implementing the properties() function.
+*/
+inline bool isEvaluated() const;
+/**
+* This function is a utility function, syntactic sugar for determining
+* whether this Expression is @p id. For example, calling <tt>is(IDIfThenClause)</tt>
+* is equivalent to <tt>id() == IDIfThenClause</tt>
+*
+* @note Do not attempt to re-implement this function. Instead, return the
+* appropriate flag in the virtual id() function.
+*/
+inline bool is(const ID id) const;
+/**
+* Determines whether this Expression has Property @p prop set.
+*
+* Calling <tt>expr->has(MyProperty)</tt> is semantically equivalent
+* to <tt>expr->properties().testFlag(MyProperty)</tt>. In
+* other words, has(), as well as is(), provides syntacti sugar
+* and makes code more readable.
+*
+* @note Do not attempt to re-implement this function. Instead, return
+* the appropriate flag by re-implementing the properties() function.
+*/
+inline bool has(const Property prop) const;
+inline bool hasDependency(const Property prop) const;
+virtual ExpressionVisitorResult::Ptr accept(const ExpressionVisitor::Ptr &visitor) const = 0;
+/**
+* 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.
+*/
+virtual ID id() const;
+/**
+* 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.
+*/
+virtual QList<QExplicitlySharedDataPointer<OptimizationPass> > optimizationPasses() const;
+/**
+* Returns the required type the context item must be an instance of.
+*
+* If this Expression requires a focus, meaning its properties()
+* function returns RequiresContextItem,
+* it must return a type from this function. If any type is ok, BuiltinTypes::item should be
+* returned.
+*
+* In other words, this function must only be re-implemented if the focus is used. The default
+* implementation performs an assert crash.
+*/
+virtual ItemType::Ptr expectedContextItemType() const;
+/**
+* If an Expression creates a focus because it has set the property CreatesFocusForLast,
+* it should override this function and make it return the ItemType that
+* the context item in the focus has.
+*
+* @returns never @c null.
+* @see announceFocusType()
+*/
+virtual ItemType::Ptr newFocusType() const;
+/**
+* @short Returns @c this.
+*/
+virtual const SourceLocationReflection *actualReflection() const;
+/**
+* Reimplementation of SourceLocationReflection::description().
+*/
+virtual QString description() const;
+/**
+* When this function is called, it signals that the parent will create
+* a focus of type @p itemType.
+*
+* This type can also be retrieved through StaticContext::contextItemType()
+* when inside typeCheck(), but in some cases this is too late. For
+* instance, a parent needs to have the static type of its child
+* properly reported before it calls its typeCheck()(and the child's
+* type is inferred from the focus).
+*
+* The default implementation delegates the call on to the children.
+*
+* This function may be called at arbitrary times, in arbitrary
+* amounts.
+*
+* If the AST node overriding this call has children, it should be
+* considered whether the default implementation should be called, such
+* that they type is announced to them too.
+*
+* The caller guarantees that @p itemType is not @c null.
+*/
+virtual void announceFocusType(const ItemType::Ptr &itemType);
+/**
+* This function take the two Expression pointers @p old and @p New, and
+* in a safe way, by handling reference counting and being aware of whether
+* the two pointers actually are different, switches the two. When compiling
+* in debug mode, informative debug messages are printed.
+*
+* This function is conceptually similar to Qt's qSwap(), but has
+* debugging functionality and also handles source locations.
+*/
+static inline void rewrite(Expression::Ptr &old,
+const Expression::Ptr &New,
+const StaticContext::Ptr &context);
+/**
+* @short Rewrites this Expression to @p to, and return @p to.
+*
+* Source location annotations are adjusted appropriately.
+*/
+inline const Expression::Ptr &rewrite(const Expression::Ptr &to,
+const StaticContext::Ptr &context) const;
+/**
+* By default 0.5 is returned.
+*/
+virtual PatternPriority patternPriority() const;
+protected:
+/**
+* @returns @c true if all operands are constant values of somekind, and are already
+* evaluated. A string literal, is a typical example.
+*/
+virtual bool compressOperands(const StaticContext::Ptr &) = 0;
+void typeCheckOperands(const StaticContext::Ptr &context);
+private:
+static Expression::Ptr invokeOptimizers(const Expression::Ptr &expr,
+const StaticContext::Ptr &context);
+/**
+* @return a StaticContext that has adopted the context item type properly
+* for this Expression.
+*/
+inline StaticContext::Ptr finalizeStaticContext(const StaticContext::Ptr &context) const;
+/**
+* @short Performs constant propagation, also called constant folding, on this expression.
+*
+* This means that it attempts to evaluate this expression at compile and returns the result value
+* appropriately as an Expression. For example, for the XPath expression
+* <tt>1 + 3</tt> would an Integer of value 4 would be returned.
+*
+* It is not checked whether constant propagation is possible, the
+* caller is responsible for this.
+*
+* @see <a href="http://en.wikipedia.org/wiki/Constant_propagation">Constant folding,
+* From Wikipedia, the free encyclopedia</a>
+*/
+Expression::Ptr constantPropagate(const StaticContext::Ptr &context) const;
+Q_DISABLE_COPY(Expression)
+};
+Q_DECLARE_OPERATORS_FOR_FLAGS(Expression::Properties)
+inline bool Expression::is(const Expression::ID i) const
+{
+return id() == i;
+}
+inline bool Expression::isEvaluated() const
+{
+return has(IsEvaluated);
+}
+inline bool Expression::has(const Expression::Property prop) const
+{
+return properties().testFlag(prop);
+}
+inline bool Expression::hasDependency(const Expression::Property prop) const
+{
+return dependencies().testFlag(prop);
+}
+inline void Expression::rewrite(Expression::Ptr &old,
+const Expression::Ptr &New,
+const StaticContext::Ptr &context)
+{
+Q_ASSERT(old);
+Q_ASSERT(New);
+if(old != New)
+{
+pDebug() << "AST REWRITE:" << old.data() << "to" << New.data()
+<< '(' << old->actualReflection() << "to" << New->actualReflection() << ", "
+<< old->description() << "to" << New->description() << ')';
+/* The order of these two lines is significant.. */
+context->addLocation(New.data(), context->locationFor(old->actualReflection()));
+old = New;
+}
+}
+inline const Expression::Ptr &Expression::rewrite(const Expression::Ptr &to,
+const StaticContext::Ptr &context) const
+{
+context->addLocation(to.data(), context->locationFor(this));
+return to;
+}
+}
+Q_DECLARE_TYPEINFO(QPatternist::Expression::Ptr, Q_MOVABLE_TYPE);
+QT_END_NAMESPACE
+QT_END_HEADER
+#endif

changeset 0	1918ee327afb
child 4	3b1da2848fc7