Unique class type Id that is safe and holds across library boundaries

Question

I would appreciate any help as C++ is not my primary language.

I have a template class that is derived in multiple libraries. I am trying to figure out a way to uniq

Answer 1

The below snippet works in VS(2015) and Release builds:

template 
struct TypeId
{
  static size_t Get()
  {
    return reinterpret_cast(&sDummy);
  }

private:
  static char sDummy;
};

template 
char TypeId::sDummy; // don't care about value

Also tried and tested on GCC v7.3 (Ubuntu 16.04) and LLVM v10.0.0 (Mac OS High Sierra).

How it works: each instantiation of the TypeId<> template gets its own, unique sDummy instance with its own, unique address. To be honest I'm not entirely sure why the function-static version didn't work in release -- I suspect identical comdat folding and optimizations.

Exercise for the reader: at least const and ref types should get the same type ID as the raw type.