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65 lines
1.7 KiB
C++
65 lines
1.7 KiB
C++
#pragma once
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#include <iosfwd>
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namespace util {
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/**
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* @brief A generic class for creating type safe handle types
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*
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* This type should be used when a function returns a handle to an internal resource instead of using an int.
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* Example:
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* @code{.cpp}
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* struct gamesnd_id_tag{};
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* typedef util::ID<gamesnd_id_tag, int, -1> gamesnd_id;
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* @endcode
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*
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* The implementation value should be very light-weight since this class is designed to be passed around by-value.
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*
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* @note This class was copied from http://www.ilikebigbits.com/blog/2014/5/6/type-safe-identifiers-in-c
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*
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* @tparam Tag A unique type tag which is used for distinguishing between two types which use the same Impl type
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* @tparam Impl The internal representation of the handle.
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* @tparam default_value The default value of the handle. If the handle has this value it is considered invalid.
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*/
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template<class Tag, class Impl, Impl default_value>
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class ID
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{
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public:
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typedef Tag tag_type;
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typedef Impl impl_type;
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static constexpr ID invalid() { return ID(); }
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// Defaults to ID::invalid()
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constexpr ID() : m_val(default_value) { }
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// Explicit constructor:
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explicit ID(Impl val) : m_val(val) { }
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inline Impl value() const { return m_val; }
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friend bool operator==(ID a, ID b) { return a.m_val == b.m_val; }
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friend bool operator!=(ID a, ID b) { return a.m_val != b.m_val; }
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friend std::ostream& operator<< (std::ostream& stream, const ID& id) {
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stream << id.value();
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return stream;
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}
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inline bool isValid() const { return m_val != default_value; }
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protected:
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Impl m_val;
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};
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struct ID_Hash
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{
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template <class Tag, class Impl, Impl default_value>
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size_t operator()(const ID<Tag, Impl, default_value> &id) const
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{
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return std::hash<Impl>{}(id.value());
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}
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};
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}
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