path: root/sal/inc/rtl/stringconcat.hxx

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/*
 * This file is part of the LibreOffice project.
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

#ifndef RTL_STRINGCONCAT_HXX
#define RTL_STRINGCONCAT_HXX

#include <rtl/stringutils.hxx>

#include <string.h>

#ifdef RTL_FAST_STRING

#ifdef RTL_STRING_UNITTEST
#define rtl rtlunittest
#endif
namespace rtl
{
#ifdef RTL_STRING_UNITTEST
#undef rtl
#endif

/*
Implementation of efficient string concatenation.

The whole system is built around two basic template classes:
- ToStringHelper< T > - for each T it can give the length of the resulting string representation and can write
    this string representation to a buffer
- O(U)StringConcat< T1, T2 > - operator+ now, instead of creating O(U)String object, returns only this helper object,
    that keeps a reference to both operator+ operands; only when converted to O(U)String it will actually create
    the resulting string object using ToStringHelper, creating directly the resulting object without any string
    intermediate objects
As all the code is inline methods, it allows for extensive optimization and will usually result in very effective code
(even surpassing strlen/strcat and equalling handwritten), while allowing for very easy and intuitive syntax.
*/

/**
@internal

Helper class for converting a given type to a string representation.
*/
template< typename T >
struct ToStringHelper
    {
    /// Return length of the string representation of the given object (if not known exactly, it needs to be the maximum).
    static int length( const T& );
    /// Add 8-bit representation of the given object to the given buffer and return position right after the added data.
    static char* addData( char* buffer, const T& );
    /// Add Unicode representation of the given object to the given buffer and return position right after the added data.
    static sal_Unicode* addData( sal_Unicode* buffer, const T& );
    /// If true, T can be used in concatenation resulting in OString.
    static const bool allowOStringConcat = false;
    /// If true, T can be used in concatenation resulting in OUString.
    static const bool allowOUStringConcat = false;
    };

inline
char* addDataHelper( char* buffer, const char* data, int length )
    {
    memcpy( buffer, data, length );
    return buffer + length;
    }

inline
sal_Unicode* addDataHelper( sal_Unicode* buffer, const sal_Unicode* data, int length )
    {
    memcpy( buffer, data, length * sizeof( sal_Unicode ));
    return buffer + length;
    }

inline
sal_Unicode* addDataLiteral( sal_Unicode* buffer, const char* data, int length )
    {
    while( length-- > 0 )
        *buffer++ = *data++;
    return buffer;
    }

inline
char* addDataCString( char* buffer, const char* str )
    {
    while( *str != '\0' )
        *buffer++ = *str++;
    return buffer;
    }

inline
sal_Unicode* addDataUString( sal_Unicode* buffer, const sal_Unicode* str )
    {
    while( *str != '\0' )
        *buffer++ = *str++;
    return buffer;
    }

template<>
struct ToStringHelper< const char* >
    {
    static int length( const char* str ) {
        return sal::static_int_cast<int>(strlen( str ));
    }
    static char* addData( char* buffer, const char* str ) { return addDataCString( buffer, str ); }
    static const bool allowOStringConcat = true;
    static const bool allowOUStringConcat = false;
    };

template<>
struct ToStringHelper< char* >
    {
    static int length( const char* str ) {
        return sal::static_int_cast<int>(strlen( str ));
    }
    static char* addData( char* buffer, const char* str ) { return addDataCString( buffer, str ); }
    static const bool allowOStringConcat = true;
    static const bool allowOUStringConcat = false;
    };

template< int N >
struct ToStringHelper< char[ N ] >
    {
    static int length( const char str[ N ] ) {
        return sal::static_int_cast<int>(strlen( str ));
    }
    static char* addData( char* buffer, const char str[ N ] ) { return addDataCString( buffer, str ); }
    static sal_Unicode* addData( sal_Unicode* buffer, const char str[ N ] ) { return addDataLiteral( buffer, str, N - 1 ); }
    static const bool allowOStringConcat = true;
    static const bool allowOUStringConcat = false;
    };

template< int N >
struct ToStringHelper< const char[ N ] >
    {
    static int length( const char str[ N ] ) { (void)str; assert( strlen( str ) == N - 1 ); return N - 1; }
    static char* addData( char* buffer, const char str[ N ] ) { return addDataHelper( buffer, str, N - 1 ); }
    static sal_Unicode* addData( sal_Unicode* buffer, const char str[ N ] ) { return addDataLiteral( buffer, str, N - 1 ); }
    static const bool allowOStringConcat = true;
    static const bool allowOUStringConcat = true;
    };

/**
@internal

Objects returned by operator+, instead of OString. These objects (possibly recursively) keep a representation of the whole
concatenation operation.
*/
template< typename T1, typename T2 >
struct OStringConcat
    {
    public:
        OStringConcat( const T1& left_, const T2& right_ ) : left( left_ ), right( right_ ) {}
        int length() const { return ToStringHelper< T1 >::length( left ) + ToStringHelper< T2 >::length( right ); }
        char* addData( char* buffer ) const { return ToStringHelper< T2 >::addData( ToStringHelper< T1 >::addData( buffer, left ), right ); }
        // NOTE here could be functions that would forward to the "real" temporary OString. Note however that e.g. getStr()
        // is not so simple, as the OString temporary must live long enough (i.e. can't be created here in a function, a wrapper
        // temporary object containing it must be returned instead).
    private:
        const T1& left;
        const T2& right;
    };

/**
@internal

Objects returned by operator+, instead of OUString. These objects (possibly recursively) keep a representation of the whole
concatenation operation.
*/
template< typename T1, typename T2 >
struct OUStringConcat
    {
    public:
        OUStringConcat( const T1& left_, const T2& right_ ) : left( left_ ), right( right_ ) {}
        int length() const { return ToStringHelper< T1 >::length( left ) + ToStringHelper< T2 >::length( right ); }
        sal_Unicode* addData( sal_Unicode* buffer ) const { return ToStringHelper< T2 >::addData( ToStringHelper< T1 >::addData( buffer, left ), right ); }
    private:
        const T1& left;
        const T2& right;
    };

template< typename T1, typename T2 >
struct ToStringHelper< OStringConcat< T1, T2 > >
    {
    static int length( const OStringConcat< T1, T2 >& c ) { return c.length(); }
    static char* addData( char* buffer, const OStringConcat< T1, T2 >& c ) { return c.addData( buffer ); }
    static const bool allowOStringConcat = ToStringHelper< T1 >::allowOStringConcat && ToStringHelper< T2 >::allowOStringConcat;
    static const bool allowOUStringConcat = false;
    };

template< typename T1, typename T2 >
struct ToStringHelper< OUStringConcat< T1, T2 > >
    {
    static int length( const OUStringConcat< T1, T2 >& c ) { return c.length(); }
    static sal_Unicode* addData( sal_Unicode* buffer, const OUStringConcat< T1, T2 >& c ) { return c.addData( buffer ); }
    static const bool allowOStringConcat = false;
    static const bool allowOUStringConcat = ToStringHelper< T1 >::allowOUStringConcat && ToStringHelper< T2 >::allowOUStringConcat;
    };

template< typename T1, typename T2 >
inline
SAL_WARN_UNUSED_RESULT
typename internal::Enable< OStringConcat< T1, T2 >, ToStringHelper< T1 >::allowOStringConcat && ToStringHelper< T2 >::allowOStringConcat >::Type operator+( const T1& left, const T2& right )
    {
    return OStringConcat< T1, T2 >( left, right );
    }

// char[N] and const char[N] need to be done explicitly, otherwise the compiler likes to treat them the same way for some reason
template< typename T, int N >
inline
SAL_WARN_UNUSED_RESULT
typename internal::Enable< OStringConcat< T, const char[ N ] >, ToStringHelper< T >::allowOStringConcat >::Type operator+( const T& left, const char (&right)[ N ] )
    {
    return OStringConcat< T, const char[ N ] >( left, right );
    }

template< typename T, int N >
inline
SAL_WARN_UNUSED_RESULT
typename internal::Enable< OStringConcat< const char[ N ], T >, ToStringHelper< T >::allowOStringConcat >::Type operator+( const char (&left)[ N ], const T& right )
    {
    return OStringConcat< const char[ N ], T >( left, right );
    }

template< typename T, int N >
inline
SAL_WARN_UNUSED_RESULT
typename internal::Enable< OStringConcat< T, char[ N ] >, ToStringHelper< T >::allowOStringConcat >::Type operator+( const T& left, char (&right)[ N ] )
    {
    return OStringConcat< T, char[ N ] >( left, right );
    }

template< typename T, int N >
inline
SAL_WARN_UNUSED_RESULT
typename internal::Enable< OStringConcat< char[ N ], T >, ToStringHelper< T >::allowOStringConcat >::Type operator+( char (&left)[ N ], const T& right )
    {
    return OStringConcat< char[ N ], T >( left, right );
    }

template< typename T1, typename T2 >
inline
typename internal::Enable< OUStringConcat< T1, T2 >, ToStringHelper< T1 >::allowOUStringConcat && ToStringHelper< T2 >::allowOUStringConcat >::Type operator+( const T1& left, const T2& right )
    {
    return OUStringConcat< T1, T2 >( left, right );
    }

template< typename T1, typename T2 >
inline
typename internal::Enable< OUStringConcat< T1, T2 >, ToStringHelper< T1 >::allowOUStringConcat && ToStringHelper< T2 >::allowOUStringConcat && internal::ConstCharArrayDetector< T1, void >::ok >::Type operator+( T1& left, const T2& right )
    {
    return OUStringConcat< T1, T2 >( left, right );
    }

template< typename T1, typename T2 >
inline
typename internal::Enable< OUStringConcat< T1, T2 >, ToStringHelper< T1 >::allowOUStringConcat && ToStringHelper< T2 >::allowOUStringConcat && internal::ConstCharArrayDetector< T2, void >::ok >::Type operator+( const T1& left, T2& right )
    {
    return OUStringConcat< T1, T2 >( left, right );
    }

#ifdef RTL_STRING_UNITTEST_CONCAT
// Special overload to catch the remaining invalid combinations. The helper struct must
// be used to make this operator+ overload a worse choice than all the existing overloads above.
struct StringConcatInvalid
    {
    template< typename T >
    StringConcatInvalid( const T& ) {}
    };
template< typename T >
inline
int operator+( const StringConcatInvalid&, const T& )
    {
    rtl_string_unittest_invalid_concat = true;
    return 0; // doesn't matter
    }
#endif

} // namespace

#endif

#endif