Comment by phire

I suspect it's actually possible to prove such an algorithm can't exist.

By definition, a ZST hold no runtime data. It does hold some compile-time data based on its existence, but after compiling, that has been type erased away.

Since a ZST holds zero bits of state, there can only be one valid instance of it. You can't have multiple different versions of the same ZST representing different things.

So if you have one, you automatically know it's going to be equal to all other instances of the same ZST type. And not equal to any other ZSTs. There is no point doing a pointer comparison, as that gives you no extra information, type ownership is enough.