Is accessing a tuple of tuples of pointers and a mutexes thread-safe

Quoting from the perfect answer to the question you linked:

However, if the parameter were const, then get would not be considered to provoke a data race with other const calls to get.

This is basically your answer. Make each and every get call (on any tuple that's not completely protected by a mutex) on a const tuple and you're safe.

This means your code as posted is not safe. Modify like so:

void baz(){    //    vvvv just being explicit here    auto const & tup = std::get<0>(static_cast<decltype(tuple) const &>(tuple));    std::lock_guard<std::mutex> lk(*std::get<2>(tup));    // Dereference std::get<0>(tup) and std::get<1>(tup),     // use the pointed to objects at will, nothing else    // Not ok, because it could interfer with the call in initialisation of tup of another thread    // auto non_const_tup = std::get<0>(tuple)}

Currently the only solution I see is using a tuple like:

std::tuple<    std::shared_pointer<std::mutex>,    std::unique_pointer<std::tuple<Foo1*, Bar1*>>    // Mutex and pointer to tuple for Foo2 and Bar2    >

The required const will stick to everything (except pointer targets).