source: trunk/src/xmlpatterns/functions/qsequencefns_p.h@ 987

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//
//  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_SequenceFNs_H
#define Patternist_SequenceFNs_H

#include "qatomiccomparator_p.h"
#include "qcomparisonplatform_p.h"
#include "qliteral_p.h"
#include "qfunctioncall_p.h"

/**
 * @file
 * @short Contains classes implementing the functions found in
 * <a href="http://www.w3.org/TR/xpath-functions/#general-seq-funcs">XQuery 1.0 and
 * XPath 2.0 Functions and Operators, 15.1 General Functions and Operators on Sequences</a>.
 *
 * @todo document that some functions have both eval funcs implented.
 *
 * @ingroup Patternist_functions
 */

QT_BEGIN_HEADER

QT_BEGIN_NAMESPACE

namespace QPatternist
{
    /**
     * @short Implements the function <tt>fn:boolean()</tt>.
     *
     * @see EBVExtractor
     * @ingroup Patternist_functions
     * @author Frans Englich <[email protected]>
     */
    class BooleanFN : public FunctionCall
    {
    public:
        virtual bool evaluateEBV(const DynamicContext::Ptr &context) const;

        /**
         * If @p reqType is CommonSequenceTypes::EBV, the type check of
         * the operand is returned. Hence, this removes redundant calls
         * to <tt>fn:boolean()</tt>.
         */
        virtual Expression::Ptr typeCheck(const StaticContext::Ptr &context,
                                          const SequenceType::Ptr &reqType);
    };

    /**
     * @short Implements the function <tt>fn:index-of()</tt>.
     *
     * @ingroup Patternist_functions
     * @author Frans Englich <[email protected]>
     */
    class IndexOfFN : public FunctionCall,
                      public ComparisonPlatform<IndexOfFN, false>
    {
    public:
        inline IndexOfFN() : ComparisonPlatform<IndexOfFN, false>()
        {
        }

        virtual Item::Iterator::Ptr evaluateSequence(const DynamicContext::Ptr &context) const;
        virtual Expression::Ptr typeCheck(const StaticContext::Ptr &context,
                                          const SequenceType::Ptr &reqType);

        inline AtomicComparator::Operator operatorID() const
        {
            return AtomicComparator::OperatorEqual;
        }
    };

    /**
     * @short Implements the functions <tt>fn:exists()</tt> and <tt>fn:empty()</tt>.
     *
     * Existence is a template value class. Appropriate implementations are achieved
     * by instantiating it with either IDExistsFN or IDEmptyFN.
     *
     * @ingroup Patternist_functions
     * @author Frans Englich <[email protected]>
     */
    template<const Expression::ID Id>
    class Existence : public FunctionCall
    {
    public:
        virtual bool evaluateEBV(const DynamicContext::Ptr &context) const
        {
            if(Id == IDExistsFN)
                return !m_operands.first()->evaluateSequence(context)->isEmpty();
            else
                return m_operands.first()->evaluateSequence(context)->isEmpty();
        }

        /**
         * Attempts to rewrite to @c false or @c true by looking at the static
         * cardinality of its operand.
         */
        virtual Expression::Ptr compress(const StaticContext::Ptr &context)
        {
            // RVCT doesn't like using template parameter in trinary operator when the trinary operator result is
            // passed directly into another constructor. 
            Q_ASSERT(Id == IDExistsFN || Id == IDEmptyFN);

            const Expression::Ptr me(FunctionCall::compress(context));

            if(me != this)
                return me;

            // RVCT doesn't like using template parameter in trinary operator when the trinary operator result is
            // passed directly into another constructor. 
            Expression::ID tempId = Id;
            const Cardinality myCard((tempId == IDExistsFN) ? Cardinality::oneOrMore() : Cardinality::empty());

            const Cardinality card(m_operands.first()->staticType()->cardinality());
            if(myCard.isMatch(card))
            { /* Since the dynamic type always is narrower than the static type or equal, and that the
                 static type is in scope, it means we will always be true. */
                return wrapLiteral(CommonValues::BooleanTrue, context, this);
            }
            else
            {
                /* Is it even possible to hit? */
                if(myCard.canMatch(card))
                {
                    return me;
                }
                else
                { /* We can never hit. */
                    return wrapLiteral(CommonValues::BooleanFalse, context, this);
                }
            }
        }
    };

    /**
     * @short Implements the function <tt>fn:distinct-values()</tt>.
     *
     * @ingroup Patternist_functions
     * @author Frans Englich <[email protected]>
     */
    class DistinctValuesFN : public FunctionCall,
                             public ComparisonPlatform<IndexOfFN, false>
    {
    public:
        inline DistinctValuesFN() : ComparisonPlatform<IndexOfFN, false>()
        {
        }

        virtual Item::Iterator::Ptr evaluateSequence(const DynamicContext::Ptr &context) const;
        /**
         * Performs necessary type checks, but also implements the optimization
         * of rewriting to its operand if the operand's cardinality is zero-or-one
         * or exactly-one.
         */
        virtual Expression::Ptr typeCheck(const StaticContext::Ptr &context,
                                          const SequenceType::Ptr &reqType);
        /**
         * @returns a type whose item type is the type of the first operand, and
         * a cardinality which is non-empty if the first operand's type is non-empty
         * and allows exactly-one. The latter is needed for operands which has the
         * cardinality 2+, since distinct-values possibly removes items from the
         * source sequence.
         */
        virtual SequenceType::Ptr staticType() const;

    protected:
        inline AtomicComparator::Operator operatorID() const
        {
            return AtomicComparator::OperatorEqual;
        }
    };

    /**
     * @short Implements the function <tt>fn:insert-before()</tt>.
     *
     * @todo docs, explain why evaluateSequence and evaluateSingleton is implemented
     *
     * @ingroup Patternist_functions
     * @author Frans Englich <[email protected]>