type_info.h

#pragma once
#include "gaia/config/config.h"
 
#include "gaia/core/hashing_policy.h"
#include "gaia/core/span.h"
 
namespace gaia {
  namespace meta {
 
    template <typename...>
    class type_group {
      inline static uint32_t s_identifier{};
 
    public:
      template <typename... Type>
      inline static const uint32_t id = s_identifier++;
    };
 
    template <>
    class type_group<void>;
 
    //----------------------------------------------------------------------
    // Type meta data
    //----------------------------------------------------------------------
 
    struct type_info final {
    private:
      constexpr static size_t find_first_of(const char* data, size_t len, char toFind, size_t startPos = 0) {
        for (size_t i = startPos; i < len; ++i) {
          if (data[i] == toFind)
            return i;
        }
        return size_t(-1);
      }
 
      constexpr static size_t find_last_of(const char* data, size_t len, char c, size_t startPos = size_t(-1)) {
        const auto minValue = startPos <= len - 1 ? startPos : len - 1;
        for (int64_t i = (int64_t)minValue; i >= 0; --i) {
          if (data[i] == c)
            return (size_t)i;
        }
        return size_t(-1);
      }
 
    public:
      template <typename T>
      static uint32_t id() noexcept {
        return type_group<type_info>::id<T>;
      }
 
      template <typename T>
      GAIA_NODISCARD static constexpr const char* full_name() noexcept {
        return GAIA_PRETTY_FUNCTION;
      }
 
      template <typename T>
      GAIA_NODISCARD static constexpr auto name() noexcept {
        // MSVC:
        //    const char* __cdecl ecs::ComponentInfo::name<struct ecs::EnfEntity>(void)
        //   -> ecs::EnfEntity
        // Clang/Clang-cl/GCC:
        //    const ecs::ComponentInfo::name() [T = ecs::EnfEntity]
        //   -> ecs::EnfEntity
 
        // Note:
        //    We don't want to use std::string_view here because it would only make it harder on compile-times.
        //    In fact, even if we did, we need to be afraid of compiler issues.
        //    Clang 8 and older wouldn't compile because their string_view::find_last_of doesn't work
        //    in constexpr context. Tested with and without LIBCPP
        //    https://stackoverflow.com/questions/56484834/constexpr-stdstring-viewfind-last-of-doesnt-work-on-clang-8-with-libstdc
        //    As a workaround find_first_of and find_last_of were implemented
 
        size_t strLen = 0;
        while (GAIA_PRETTY_FUNCTION[strLen] != '\0')
          ++strLen;
 
        std::span<const char> name{GAIA_PRETTY_FUNCTION, strLen};
        const auto prefixPos = find_first_of(name.data(), name.size(), GAIA_PRETTY_FUNCTION_PREFIX);
        const auto start = find_first_of(name.data(), name.size(), ' ', prefixPos + 1);
        const auto end = find_last_of(name.data(), name.size(), GAIA_PRETTY_FUNCTION_SUFFIX);
        return name.subspan(start + 1, end - start - 1);
      }
 
      template <typename T>
      GAIA_NODISCARD static constexpr auto hash() noexcept {
#if GAIA_COMPILER_MSVC && _MSC_VER <= 1916
        GAIA_MSVC_WARNING_PUSH()
        GAIA_MSVC_WARNING_DISABLE(4307)
#endif
 
        auto n = name<T>();
        return core::calculate_hash64(n.data(), n.size());
 
#if GAIA_COMPILER_MSVC && _MSC_VER <= 1916
        GAIA_MSVC_WARNING_PUSH()
#endif
      }
    };
 
  } // namespace meta
} // namespace gaia