handle.hpp

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#pragma once
 
#include <unordered_map>
#include <cstdint>
 
namespace HandleSystem
{
using HandleId = uint32_t;
 
inline HandleId &nextId()
{
    static HandleId id = 1;
    return id;
}
 
template <typename T> struct Table
{
    static std::unordered_map<HandleId, T> &idToHandle()
    {
        static std::unordered_map<HandleId, T> map;
        return map;
    }
 
    static std::unordered_map<T, HandleId> &handleToId()
    {
        static std::unordered_map<T, HandleId> map;
        return map;
    }
};
 
template <typename T> inline HandleId store(T handle)
{
    if (!handle)
        return 0;
 
    auto &h2i = Table<T>::handleToId();
    auto &i2h = Table<T>::idToHandle();
 
    auto it = h2i.find(handle);
    if (it != h2i.end())
        return it->second;
 
    HandleId id = nextId()++;
    h2i[handle] = id;
    i2h[id] = handle;
    return id;
}
 
template <typename T> inline T resolve(HandleId id)
{
    if (id == 0)
        return T{};
 
    auto &i2h = Table<T>::idToHandle();
    auto  it = i2h.find(id);
    if (it == i2h.end())
        return T{};
 
    return it->second;
}
 
template <typename T> inline void remove(HandleId id)
{
    auto &i2h = Table<T>::idToHandle();
    auto &h2i = Table<T>::handleToId();
 
    auto it = i2h.find(id);
    if (it == i2h.end())
        return;
 
    h2i.erase(it->second);
    i2h.erase(it);
}
} // namespace HandleSystem