functiondecls.hpp

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//==================================================================================================
/// \file
/// This header-file is part of module \alib_boxing of the \aliblong.
///
/// Copyright 2013-2026 A-Worx GmbH, Germany.
/// Published under #"mainpage_license".
//==================================================================================================
 
ALIB_EXPORT namespace alib {  namespace boxing  {
class Box;
 
//==================================================================================================
/// This built-in #"alib_boxing_functions;box function" constitutes the concept of
/// "nullable types". Nullable types are pointer types, array types and custom types that are
/// nullable. Arithmetical types are never \e nulled, even if they contain value \c 0 or \c 0.0.
///
/// A default implementation is given, which returns \c false (not <em>nulled</em>!) if the first word in
/// the placeholder is not \c 0. Hence this works for array and pointer types.
///
/// A constant function return \c true is given with the static method #"ConstantTrue". This function
/// is set as the specific implementation for all arithmetical types, as well as for type \c bool.
///
/// \note
///   The reason why this function is not declared as \b FIsNull, but instead is negated, is that
///   if any function is called on a #"alib_boxing_more_void_void;void box", a
///   default value is returned. The default value of \c bool is \c false, which probably better
///   fits - even if conceptually a void box is undefined and therefore neither \e nulled or not.
//==================================================================================================
struct FIsNotNull {
    /// Signature of the invokable function.
    ///
    /// @param  self The box that the function was invoked on.
    /// @return Return \c false if a boxed value is \e nulled, \c true otherwise.
    using Signature = bool (*) ( const Box& self );
 
    /// This implementation of the function signature returns constant \c true.
    /// It may be registered with custom types that do not provide the concept of being \e nulled.
    /// #"alib_mod_bs;Bootstrapping" function
    /// #"boxing::bootstrap" registers this implementation with type \c bool and all integral,
    /// floating point and character types.
    ///
    /// @return Constant \c true.
    ALIB_DLL
    static bool ConstantTrue( const Box& );
};
 
 
//==================================================================================================
/// This function returns a hashcode on contents of the box. This is useful if boxes are to
/// be used as key-values of containers like \c std::unordered_map or
/// #"HashTable".
///
/// Its default implementation creates a hash code using the raw placeholder values and
/// in case of array types over the array memory used.
///
/// A templated version that compares the first N-bytes is given with #"UsePlaceholderBytes".
/// Because the number of bytes to use are given with the template parameter, the method compiles
/// to shortest code. It is registered with all fundamental types.
///
/// \note
///   Compatibility header #"F;ALib.Boxing.StdFunctors.H" specializes
///   functors \c std::hash, \c std::equal_to and \c std::less for use with containers of the
///   C++ standard library.
///
/// \see
///   Method #"Box::Hashcode", which calls this function.
//==================================================================================================
struct FHashcode {
    /// Signature of the invokable function.
    ///
    /// @param  self The box that the hash code is to be calculated for.
    /// @return The hash code.
    using Signature = size_t (*) ( const Box& self );
 
    /// Templated hash function usable with types boxed as values.
    /// For pointer types, a custom variant that collects type-specific hashable data is recommended.
    ///
    /// @tparam N    The number of bytes to check.
    /// @param  self The box to calculate a hash code for.
    /// @return The hash code.
    template<size_t N>
    static size_t UsePlaceholderBytes( const Box& self );
 
};
 
 
//==================================================================================================
/// This function compares two boxes.
///
/// A default implementation is #"BootstrapRegisterDefault;registered" that compares the types
/// (#"Box::IsSameType") and if equal, with arrays compares the array's length,
/// \e nulled state and finally the contents using \c memcmp.<br>
/// For non-array types, it compares the relevant bytes in the placeholder.
/// The number of leading relevant bytes is available with method
/// #"Box::GetPlaceholderUsageLength".
///
/// Type-specific implementations are given and registered for fundamental types. Integrals
/// of different sizes and floating point values will be compared by using
/// #"Box::UnboxSignedIntegral", #"Box::UnboxUnsignedIntegral" and
/// #"Box::UnboxFloatingPoint" and appropriate casting.
/// In the case of floating point comparison, an epsilon distance is duly taken into account.
///
/// For custom types, with #".ComparableTypes", a templated implementation is suggested: Rather than
/// implementing a specific box-function, the custom type should implement \c operator== and register
/// an instantiation of the templated function.
///
/// \see
///   Method #"Box::operator==", which calls this function.
//==================================================================================================
struct FEquals {
    /// Signature of the invokable function.
    ///
    /// @param self The box that the function was invoked on.
    /// @param rhs  The box to compare.
    /// @return Return value and type is implementation specific.
    using Signature = bool (*) ( const Box& self, const Box& rhs);
 
 
    #if DOXYGEN
    /// Templated implementation of the function signature, usable with boxable types which have
    /// <c>operator==</c> implemented.
    ///
    /// \note
    ///   This method internally is provided twice: once for types boxed as pointers and one for
    ///   types boxed as values, and selected using keyword \c requires.<br>
    ///   If a type is boxed as a pointer, then \p{TComparable} has to be given as such
    ///   pointer-type.
    ///   For comparison, the unboxed pointers will be dereferenced.
    ///   If one is \e nulled, \c false is returned, if both are \e nulled, true.
    ///
    /// \see
    ///   Macro #"ALIB_BOXING_DEFINE_FEQUALS_FOR_COMPARABLE_TYPE".
    ///
    /// @tparam TComparable  The mapped type that can be compared using <c>operator==</c>.
    /// @param self The box that the function was invoked on.
    /// @param rhs  The boxed value to compare.
    ///
    /// @return \c true if \p{self} equals \p{rhs}, \c false otherwise.
    template<typename TComparable>
    static
    bool  ComparableTypes( const Box& self, const Box& rhs );
 
    #else
    template<typename TComparable>
    requires (!std::is_pointer_v<TComparable> )
    static bool ComparableTypes( const Box& self, const Box& rhs );
 
    template<typename TComparable>
    requires (std::is_pointer_v<TComparable>)
    static bool ComparableTypes( const Box& self, const Box& rhs );
    #endif
};
 
 
//==================================================================================================
/// This function provides a relational comparison of two boxes.
///
/// A default implementation is #"BootstrapRegisterDefault;registered" that compares the types.
/// If they are equal, the first \c uinteger values in the placeholders are compared.
/// Specifics for array types are \b not implemented with that default version.
///
/// If the types are not the same, the result of the comparison of the runtime type information
/// object is returned. For this, method #"Box::TypeID" is invoked on both boxes
/// and to allow <c>operator<</c> on those, \c std::type_index is applied.
/// This leads to a "nested" sort order, with the type information being the outer order and
/// the boxed data being the inner.<br>
/// To keep this overall order intact, type-specific implementations should use the following
/// implementation scheme:
///
///      if( rhs.IsType<AComparableType1>() )
///          return MyCompare( self.Unbox<MyType>, rhs.Unbox<AComparableType1>();
///
///      if( rhs.IsType<AComparableType2>() )
///          return MyCompare( self.Unbox<MyType>, rhs.Unbox<AComparableType2>();
///
///      if( ...
///          return ...
///
///      return std::type_index( self.TypeID() ) < std::type_index( rhs.TypeID() );
///
/// With this scheme in place, for example, \c std::sort will work properly on containers of boxes of
/// mixed types. The following sample demonstrates this. It uses a specialization of
/// \c std::less<T> for type #"%Box". This is found in a compatibility header:
///
///   \snippet "DOX_BOXING.cpp"     DOX_BOXING_FISLESS_INCLUDES
///
/// With that, the following code compiles fine:
///   \snippet "DOX_BOXING.cpp"     DOX_BOXING_FISLESS
///
/// It generates the following output:
///
///   \snippet "DOX_BOXING_FISLESS.txt"     OUTPUT
///
/// As can be seen from the result, a proper "outer" sorting is in place. Nevertheless,
/// floating-point and integral values follow the inner sorting.
/// This is because specific implementations of the functions are registered for all arithmetic
/// types, which allow comparisons of mixed types.
/// The same is true for the different C++ character types.
///
/// \note
///   It is a matter of the compiler (and cannot be determined by the user code) how the
///   types are sorted (outer sorting).<br>
///   Furthermore, the default implementation that simply compares the first #"%lang::uinteger" of
///   the placeholder is unlikely to produce "reasonable" results.
///
/// Type-specific implementations are given and registered for fundamental types. Integrals
/// of different sizes and floating point values will be compared by using
/// #"Box::UnboxSignedIntegral", #"Box::UnboxUnsignedIntegral" and
/// #"Box::UnboxFloatingPoint" and appropriate casting.
///
/// If module \alib_strings is included in the \alibbuild, an implementation for
/// arrays of #"characters::nchar", #"characters::wchar" and #"characters::xchar" is given.
///
/// For custom types, with #".ComparableTypes", a templated implementation is suggested: Rather than
/// implementing a specific box-function, the custom type should implement \c operator< and register
/// an instantiation of the templated function.
///
/// \see
///   Method #"Box::operator<", which calls this function.
//==================================================================================================
struct FIsLess {
    /// Signature of the invokable function.
    ///
    /// @param self The box that the function was invoked on.
    /// @param rhs  The box to compare.
    /// @return Return value and type is implementation specific.
    using Signature = bool (*) ( const Box& self, const Box& rhs);
 
 
    #if DOXYGEN
    /// Templated implementation for function #"FIsLess", usable with boxable types
    /// which have <c>operator<</c> implemented.
    ///
    /// \note
    ///   This method internally is provided twice, once for types boxed as pointers and one for
    ///   types boxed as values, and selected using template programming.<br>
    ///   If a type is boxed as pointer, then \p{TComparable} has to be given as such a pointer
    ///   type.
    ///   For comparison, the unboxed pointers will be dereferenced. If both are \e nulled, \c false
    ///   is returned if only \p{self} is \e nulled, \c true and if only \p{rhs} is \e nulled,
    ///   then \c false.
    ///
    /// \see
    ///   Macro #"ALIB_BOXING_DEFINE_FISLESS_FOR_COMPARABLE_TYPE".
    ///
    /// @tparam TComparable  The mapped type that can be compared using <c>operator<</c>.
    /// @param self The box that the function was invoked on.
    /// @param rhs  The boxed value to compare.
    ///
    /// @return \c true if \p{self} equals \p{rhs}, \c false otherwise.
    template<typename TComparable>
    static
    bool  ComparableTypes( const Box& self, const Box& rhs );
 
    #else
    template<typename TComparable>
    requires (!std::is_pointer_v<TComparable> )
    static bool ComparableTypes( const Box& self, const Box& rhs );
 
    template<typename TComparable>
    requires (std::is_pointer_v<TComparable> )
    static bool ComparableTypes( const Box& self, const Box& rhs );
    #endif
};
 
 
#if ALIB_MONOMEM
 
//==================================================================================================
/// This type declares a built-in #"alib_boxing_functions;box-function".<br>
/// Besides mandatory parameter \p{self}, implementations expect a reference to an allocator of type
/// #"MonoAllocator". With that, a deep copy of the boxed object can be allocated.
///
/// The function is provided for use-cases where boxes have to "survive" the end of
/// the life-cycle of the original object.
///
/// A default implementation of this function is provided. While this just does nothing
/// for non-array types, with array types, the complete contents of the array is cloned.
/// With this in place, all boxed character arrays (strings) are cloned.
/// This is done regardless if it is necessary or not. For example, if the boxed string
/// was created from a C++ string literal, a deep copy is unnecessary.
/// While this imposes a little overhead, there is no way to avoid this because the origin of a
/// boxed array cannot be determined.
///
/// \attention
///   Only objects that do not need to be destructed are allowed to be cloned using the
///   monotonic allocator given. This is because \b no destructor will be invoked for boxed objects
///   (which is true in general for \alib_boxing).<br>
///   Of course a custom implementation could create and allocate the object in a custom place,
///   that allows later destruction. Alternatively, a custom method could just ensure that
///   an object will not be deleted, e.g., by increasing a usage counter and leave the given box
///   untouched.
///
/// \note
///   Today, this is the only box-function type found within \alib, that requires a
///   mutable "this"  pointer (aka a non constant parameter \p{self}).<br>
///   Consequently, if the function is called, the compiler selects the non-constant version of
///   method #"Box::Call".<br>
///   Furthermore it has to be noted, that an invocation of this function might change the type
///   together with the contents of \p{self}. Therefore, results of any already performed
///   type-guessing are not valid after an invocation.
///
/// \attention
///   If a mapped type has no specialization for this function, there are three possibilities:
///   1. The original value is not deleted during the life-cycle of the box.
///   2. The type was boxed as a value type (or, very unlikely, otherwise is safe to be unboxed,
///      even after the deletion of the original value).
///   3. Undefined behavior (crash) due to unboxing the value after deletion of the original
///      object.
///
/// \par Availability
///   This box-function is available only if the module \alib_monomem is included in the
///   \alibbuild.
//==================================================================================================
struct FClone {
    /// Signature of the box-function.
    ///
    /// @param self       The mutable box that the function was invoked on.
    /// @param allocator  A monotonic allocator that may be used for cloning.
    using Signature = void (*) ( boxing::Box& self, MonoAllocator& allocator );
};
#endif
 
//==================================================================================================
/// This is one of the built-in #"alib_boxing_functions;box-functions" of \alib_boxing_nl.
/// This function is used to give an answer to the question if a boxed value represents a boolean
/// value \c true or \c false. This is useful if "yes/no" decisions should be taken based on
/// arbitrary boxed values.
///
/// A default implementation is registered which for non-array types just interprets the first
/// integral value in the #"boxing::Placeholder": If it is not \c 0, \c true is returned, \c false
/// otherwise.<br>
/// For array types, the default implementation returns \c true if method
/// #"Box::UnboxLength" returns a value different to \c 0, otherwise \c false is returned.
//==================================================================================================
struct FIsTrue {
    /// Signature of the invokable function.
    ///
    /// @param  self The box that the function was invoked on.
    /// @return Return value and type is implementation specific.
    using Signature = bool (*) ( const Box& self);
};
 
 
#if ALIB_STRINGS
//==================================================================================================
/// Implementations of this #"alib_boxing_functions;box-function" write the content of the
/// data stored in the box to the given #"%AString" object.
///
/// A default implementation is registered. This writes out the raw value of the first
/// \c uinteger field of the boxes' #"boxing::Placeholder" in hexadecimal format.
/// For pointer types, such raw value reflects the memory address of the boxable.
/// In debug-compilations, in addition, the type name of the boxed value is written.
///
/// Templated static method #".Appendable" can be used to avoid implementations for those mapped types
/// that specialized type-traits functor #"AppendableTraits" that makes values of the type
/// usable with #"TAString::Append(const TAppendable&)" already.
///
/// \note
///   This is a templated (!) function declaration that defines three different box-functions at
///   once, namely \b FAppend<character>, \b FAppend<characters::complementChar> and
///   \b FAppend<strangeChar>.
///
/// This box-function is usually invoked only indirectly, by "appending" a box to an #"%AString",
/// as shown here:
///
///      Box     box= 42;
///      AString text;
///
///      text << "The answer is: "; // appends a string literal
///      text << box;               // translates to: box.Call<FAppend<character>>( text )
///
/// \par Availability
///   This box-function is available only if the module \alib_strings is included in the \alibbuild.
///
/// \see
///    - Manual chapter #"alib_boxing_strings_fappend"
///    - Chapter #"alib_format_custom_types" of
///      the Programmer's Manual of \alib_format, which gives
///      a sample implementation of this function, and introduces a more powerful
///      box-function #"FFormat".
///
/// @tparam TChar      The character type of the destination #"^AString" given with parameter
///                    \p{target}.
/// @tparam TAllocator The allocator type, as prototyped with class #"lang::Allocator".
//==================================================================================================
template<typename TChar, typename TAllocator>
struct FAppend {
    /// Signature of the invokable function.
    ///
    /// @param  self   The box that the function was invoked on.
    /// @param  target The target #"%AString" of character type \p{TChar}.
    using Signature = void (*) ( const Box& self, strings::TAString<TChar, TAllocator>& target );
 
 
    #if DOXYGEN
    /// Static templated implementation of #"FAppend" for boxed types which are appendable.
    ///
    /// Once a type is made \e appendable by specializing type-traits functor
    /// #"AppendableTraits", then this static templated function can be used "as is"
    /// and registered with the corresponding mapped type.
    ///
    /// \note
    ///   This method internally is provided twice, once for types boxed as pointers and one for
    ///   types boxed as values, and selected using template programming.<br>
    ///   If a type is boxed as a pointer, then \p{TComparable} has to be given as such a pointer
    ///   type.
    ///   For comparison, the unboxed pointers will be dereferenced. This means that
    ///   it is believed that #"AppendableTraits" is specialized for the non-pointer type.
    ///   If this is not the case, then two options exist:
    ///   1. Specialize functor #"AppendableTraits" for the non-pointer type in parallel.
    ///   2. Do not use this inlined implementation, but rather provide a custom one that
    ///      does not dereference unboxed pointers.
    ///
    /// \see
    ///  Macros
    ///  - ALIB_BOXING_BOOTSTRAP_REGISTER_FAPPEND_FOR_APPENDABLE_TYPE
    ///  - ALIB_BOXING_BOOTSTRAP_REGISTER_FAPPEND_FOR_APPENDABLE_TYPE_N
    ///  - ALIB_BOXING_BOOTSTRAP_REGISTER_FAPPEND_FOR_APPENDABLE_TYPE_W
    ///  - ALIB_BOXING_BOOTSTRAP_REGISTER_FAPPEND_FOR_APPENDABLE_TYPE_X
    ///
    /// @tparam TAppendable   The "appendable" mapped box type that the function is to be implemented
    ///                       for.
    /// @param  self   The box that the function was invoked on.
    /// @param  target The target #"%AString" of character type \p{TChar}.
    template<typename TAppendable>
    inline static
    void Appendable( const Box& self, strings::TAString<TChar, TAllocator>& target );
    #else
 
    template<typename TAppendable>
    requires ( !std::is_pointer_v<TAppendable> )
    static void  Appendable( const Box& self, strings::TAString<TChar, TAllocator>& target );
 
    template<typename TAppendable>
    requires ( std::is_pointer_v<TAppendable> )
    static void  Appendable( const Box& self, strings::TAString<TChar, TAllocator>& target );
 
    #endif
 
 
    /// Implementation template for box-function #"FAppend" for appendable types wrapped
    /// in \c std::reference_wrapper to
    /// #"alib_boxing_customizing_identity;bypass custom boxing".
    ///
    /// This static function template can be used for any type \p{TAppendable} that has a
    /// specialization of functor #"AppendableTraits" defined and that becomes boxed
    /// in the wrapper type.
    ///
    /// @tparam TAppendable   The "appendable" wrapped mapped box type that the function is to be
    ///                       implemented for.
    /// @param self   The box that the function was invoked on.
    /// @param target The target #"%AString" object.
    template<typename TAppendable>
    inline static
    void WrappedAppendable( const Box& self, strings::TAString<TChar, TAllocator>& target);
}; // FAppend
#endif //ALIB_STRINGS
 
}
 
/// Type alias in namespace #"%alib".
using     FHashcode     =   boxing::FHashcode;
 
#if ALIB_MONOMEM
/// Type alias in namespace #"%alib".
using     FClone        =   boxing::FClone;
#endif
 
/// Type alias in namespace #"%alib".
using     FEquals       =   boxing::FEquals;
 
/// Type alias in namespace #"%alib".
using     FIsNotNull    =   boxing::FIsNotNull;
 
/// Type alias in namespace #"%alib".
using     FIsLess       =   boxing::FIsLess;
 
/// Type alias in namespace #"%alib".
using     FIsTrue       =   boxing::FIsTrue;
 
#if ALIB_STRINGS
/// Type alias in namespace #"%alib".
template<typename TChar, typename TAllocator>
using     FAppend       =   boxing::FAppend<TChar, TAllocator>;
#endif
 
} // namespace [alib::boxing]