entt/docs/shared.md

EnTT and shared libraries

To make sure that an application and a shared library that use both EnTT can interact correctly when symbols are hidden by default, there are some tricks to follow.
In particular and in order to avoid undefined behaviors, all the instantiation of the Family class template shall be made explicit along with the system-wide specifier to use to export them.

At the time I'm writing this document, the classes that use internally the above mentioned class template are Dispatcher, Emitter and Registry. Therefore and as an example, if you use the Registry class template in your shared library and want to set symbols visibility to hidden by default, the following lines are required to allow it to function properly with a client that also uses the Registry somehow:

• On GNU/Linux:

  namespace entt {
    template class __attribute__((visibility("default"))) Family<struct InternalRegistryTagFamily>;
    template class __attribute__((visibility("default"))) Family<struct InternalRegistryComponentFamily>;
    template class __attribute__((visibility("default"))) Family<struct InternalRegistryHandlerFamily>;
  }
  

• On Windows:

  namespace entt {
    template class __declspec(dllexport) Family<struct InternalRegistryTagFamily>;
    template class __declspec(dllexport) Family<struct InternalRegistryComponentFamily>;
    template class __declspec(dllexport) Family<struct InternalRegistryHandlerFamily>;
  }
  

Otherwise, the risk is that type identifiers are different between the shared library and the application and this will prevent the whole thing from functioning correctly for obvious reasons.