stdtypeinfofunctors.inl

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//==================================================================================================
/// \file
/// This header-file is part of module \alib_lang of the \aliblong.
///
/// \emoji :copyright: 2013-2025 A-Worx GmbH, Germany.
/// Published under \ref mainpage_license "Boost Software License".
//==================================================================================================
ALIB_EXPORT namespace alib::lang {
 
//==================================================================================================
/// This is a simple struct that features the use of <c>std::type_info</c> as key values of
/// container types like hash tables and sets. For this, this struct provides inner
/// functors \b hash, \b equal_to and \b less.
///
/// If for example a <c>std::unordered_map</c> should be instantiated with run-time type
/// information as the hash key, a definition looks as follows:
///
///      std::unordered_map<TypeFunctors::Key,      MyMappedType,
///                         TypeFunctors::Hash,
///                         TypeFunctors::EqualTo                  > myMap;
///
/// Note that the key type evaluates to <c>const std::type_info*</c>, hence pointers to
/// the structs have to be given when interfacing with the container.
//==================================================================================================
struct TypeFunctors
{
    /// The key type
    using Key= const ::std::type_info*;
 
    //==============================================================================================
    /// Hash code functor for type <c>const std::type_info*</c>.
    //==============================================================================================
    struct Hash
    {
        /// Invokes <c>std::type_info::hash_code</c> on the wrapped type.
        /// @param typeinfo  Pointer to the run-time type information struct.
        /// @return The hash code
        size_t operator()( Key typeinfo ) const
        {
            return typeinfo->hash_code();
        }
    };
 
    //==============================================================================================
    /// Comparison functor for type <c>const std::type_info*</c>.
    //==============================================================================================
    struct EqualTo
    {
        /// Invokes <c>operator ==</c> with \p{lhs} and \p{rhs}.
        /// @param lhs  The left-hand side value.
        /// @param rhs  The right-hand side value.
        /// @return \c true if the objects represent the same type, \c false otherwise.
        bool operator()( Key lhs, Key rhs ) const
        {
            return *lhs == *rhs;
        }
    };
 
    //==============================================================================================
    /// Comparison functor for type <c>const std::type_info*</c>.
    //==============================================================================================
    struct Less
    {
        /// Invokes <c>std::type_index::operator<</c> on corresponding temporaries created from
        /// \p{lhs} and \p{rhs}.
        /// @param lhs  The left-hand side value.
        /// @param rhs  The right-hand side value.
        /// @return \c true if \p{lhs} is "less" than \p{rhs}, \c false otherwise.
        bool operator()( Key lhs, Key rhs ) const
        {
            return ::std::type_index( *lhs ) < ::std::type_index( *rhs );
        }
    };
}; // struct TypeFunctors
 
} // namespace [alib::lang]