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