src/xmlpatterns/expr/qcastingplatform_p.h
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     1 /****************************************************************************
       
     2 **
       
     3 ** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
       
     4 ** All rights reserved.
       
     5 ** Contact: Nokia Corporation (qt-info@nokia.com)
       
     6 **
       
     7 ** This file is part of the QtXmlPatterns module of the Qt Toolkit.
       
     8 **
       
     9 ** $QT_BEGIN_LICENSE:LGPL$
       
    10 ** No Commercial Usage
       
    11 ** This file contains pre-release code and may not be distributed.
       
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    16 ** GNU Lesser General Public License Usage
       
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    20 ** packaging of this file.  Please review the following information to
       
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    37 **
       
    38 ** $QT_END_LICENSE$
       
    39 **
       
    40 ****************************************************************************/
       
    41 
       
    42 //
       
    43 //  W A R N I N G
       
    44 //  -------------
       
    45 //
       
    46 // This file is not part of the Qt API.  It exists purely as an
       
    47 // implementation detail.  This header file may change from version to
       
    48 // version without notice, or even be removed.
       
    49 //
       
    50 // We mean it.
       
    51 
       
    52 #ifndef Patternist_CastingPlatform_H
       
    53 #define Patternist_CastingPlatform_H
       
    54 
       
    55 #include "qatomiccasterlocator_p.h"
       
    56 #include "qatomiccaster_p.h"
       
    57 #include "qatomicstring_p.h"
       
    58 #include "qatomictype_p.h"
       
    59 #include "qbuiltintypes_p.h"
       
    60 #include "qcommonsequencetypes_p.h"
       
    61 #include "qpatternistlocale_p.h"
       
    62 #include "qqnamevalue_p.h"
       
    63 #include "qschematypefactory_p.h"
       
    64 #include "qstaticcontext_p.h"
       
    65 #include "qvalidationerror_p.h"
       
    66 
       
    67 QT_BEGIN_HEADER
       
    68 
       
    69 QT_BEGIN_NAMESPACE
       
    70 
       
    71 namespace QPatternist
       
    72 {
       
    73     /**
       
    74      * @short Provides casting functionality for classes, such as CastAs or NumberFN, which
       
    75      * needs to perform casting.
       
    76      *
       
    77      * Classes which need to perform casting can simply from this class and gain
       
    78      * access to casting functinality wrapped in a convenient way. At the center of this
       
    79      * class is the cast() function, which is used at runtime to perform the actual cast.
       
    80      *
       
    81      * The actual circumstances where casting is used, such as in the 'castable as'
       
    82      * expression or the <tt>fn:number()</tt> function, often have other things to handle as well,
       
    83      * error handling and cardinality checks for example. This class handles only casting
       
    84      * and leaves the other case-specific details to the sub-class such that this class only
       
    85      * do one thing well.
       
    86      *
       
    87      * This template class takes two parameters:
       
    88      * - TSubClass This should be the class inheriting from CastingPlatform.
       
    89      * - issueError if true, errors are issued via ReportContext, otherwise
       
    90      *   ValidationError instances are returned appropriately.
       
    91      *
       
    92      * The class inheriting CastingPlatform must implement the following function:
       
    93      * @code
       
    94      * ItemType::Ptr targetType() const
       
    95      * @endcode
       
    96      *
       
    97      * that returns the type that should be cast to. The type must be an AtomicType.
       
    98      * Typically, it is appropriate to declare this function @c inline.
       
    99      *
       
   100      * A sub-class calls prepareCasting() at compile time(such that CastingPlatform can attempt
       
   101      * to lookup the proper AtomicCaster) and then it simply uses the cast() function at runtime. The
       
   102      * function targetType() must be implemented such that CastingPlatform knows
       
   103      * what type it shall cast to.
       
   104      *
       
   105      * @see ValueFactory
       
   106      * @author Frans Englich <frans.englich@nokia.com>
       
   107      * @ingroup Patternist_expressions
       
   108      */
       
   109     template<typename TSubClass, const bool issueError>
       
   110     class CastingPlatform
       
   111     {
       
   112     protected:
       
   113         /**
       
   114          * @note issueCastError() depends on the default value.
       
   115          */
       
   116         inline CastingPlatform(const ReportContext::ErrorCode code = ReportContext::FORG0001) : m_errorCode(code)
       
   117         {
       
   118         }
       
   119 
       
   120         /**
       
   121          * Attempts to cast @p sourceValue to targetType(), and returns
       
   122          * the created value. Remember that prepareCasting() should have been
       
   123          * called at compile time, otherwise this function will be slow.
       
   124          *
       
   125          * Error reporting is done in two ways. If a cast fails because
       
   126          * of an error in lexical representation a ValidationError is returned.
       
   127          * If the cause of failure is that the casting combination is invalid(such as
       
   128          * when attempting to cast @c xs:date to @c xs:integer), a ValidationError
       
   129          * is returned if @c false was passed in the template instantiation,
       
   130          * an error is issued via @p context.
       
   131          *
       
   132          * @param sourceValue the value to cast. Must be non @c null.
       
   133          * @param context the usual ReportContext, used for error reporting.
       
   134          * @returns the new value which was the result of the cast. If the
       
   135          * cast failed, an ValidationError is returned.
       
   136          */
       
   137         Item cast(const Item &sourceValue,
       
   138                   const ReportContext::Ptr &context) const;
       
   139 
       
   140         /**
       
   141          * This function should be called at compiled time, it attempts to determine
       
   142          * what AtomicCaster that should be used when casting from @p sourceType to
       
   143          * targetType(). If that is not possible, because the @p sourceType is
       
   144          * @c xs:anyAtomicType for instance, the AtomicCaster lookup will done at
       
   145          * runtime on a case-per-case basis.
       
   146          *
       
   147          * @returns @c true if the requested casting combination is valid or might be valid.
       
   148          * If it is guranteed to be invalid, @c false is returned.
       
   149          */
       
   150         bool prepareCasting(const ReportContext::Ptr &context,
       
   151                             const ItemType::Ptr &sourceType);
       
   152 
       
   153         /**
       
   154          * Checks that the targetType() is a valid target type for <tt>castable as</tt>
       
   155          * and <tt>cast as</tt>. For example, that it is not abstract. If the type is
       
   156          * invalid, an error is raised via the @p context. Note that it is assumed the type
       
   157          * is atomic.
       
   158          */
       
   159         void checkTargetType(const ReportContext::Ptr &context) const;
       
   160 
       
   161     private:
       
   162         inline Item castWithCaster(const Item &sourceValue,
       
   163                                    const AtomicCaster::Ptr &caster,
       
   164                                    const ReportContext::Ptr &context) const;
       
   165 
       
   166         /**
       
   167          * Locates the caster for casting values of type @p sourceType to targetType(), if
       
   168          * possible.
       
   169          *
       
   170          * @p castImpossible is not initialized. Initialize it to @c false.
       
   171          */
       
   172         static AtomicCaster::Ptr locateCaster(const ItemType::Ptr &sourceType,
       
   173                                               const ReportContext::Ptr &context,
       
   174                                               bool &castImpossible,
       
   175                                               const SourceLocationReflection *const location,
       
   176                                               const ItemType::Ptr &targetType);
       
   177     private:
       
   178         inline Item castWithCaster(const Item &sourceValue,
       
   179                                    const AtomicCaster::Ptr &caster,
       
   180                                    const DynamicContext::Ptr &context) const;
       
   181 
       
   182 
       
   183         inline ItemType::Ptr targetType() const
       
   184         {
       
   185             Q_ASSERT(static_cast<const TSubClass *>(this)->targetType());
       
   186             return static_cast<const TSubClass *>(this)->targetType();
       
   187         }
       
   188 
       
   189         void issueCastError(const Item &validationError,
       
   190                             const Item &sourceValue,
       
   191                             const ReportContext::Ptr &context) const;
       
   192 
       
   193         Q_DISABLE_COPY(CastingPlatform)
       
   194         AtomicCaster::Ptr m_caster;
       
   195         const ReportContext::ErrorCode m_errorCode;
       
   196     };
       
   197 
       
   198 #include "qcastingplatform.cpp"
       
   199 
       
   200 }
       
   201 
       
   202 QT_END_NAMESPACE
       
   203 
       
   204 QT_END_HEADER
       
   205 
       
   206 #endif