--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/xmlpatterns/expr/qexpression_p.h Mon Jan 11 14:00:40 2010 +0000
@@ -0,0 +1,909 @@
+/****************************************************************************
+**
+** 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