Does the one-STL-per-app recommendation always apply no matter what?

[sonicdebris]

I am integrating a pre-built library from a 3rd-party vendor, and I have the opportunity to shape some aspects of the dependency consumption with them.

The vendor's library uses the STL, and the guidelines advise to have both libraries (mine and the vendor's) link to the STL dynamically (ie. with c++_shared), and making sure they link to "compatible" versions.

While reviewing my options, I realised that, in terms of "compatibility peace of mind", it might be better to actually have each library link to the STL statically (c++_static), provided that:

• My library links to the vendor's library dynamically (ie. the vendor provides us with a .so)
• The vendor's API is strictly C (no STL objects crossing the boundaries, but also no allocation / deallocation / exceptions across boundaries)
• The vendor's library hides all symbols but the ones explicitly exposed by the API (so that the STL symbols stay hidden and "confined" inside the vendor library, never seen by mine)
• I hide symbols from my library in the same way (I think this is not stricly necessary but can't hurt and I do it already anyway).

Putting aside binary size considerations, this would free both us and the vendor from any effort in keeping the STL "aligned". Is my understanding correct? Is there anything I am missing in reasoning about this?

[nickdesaulniers]

Caveat emptor: I have never tried this.

I think this can be made to work if you're extra careful about:

1. statically link libc++
2. hide the symbols from libc++
3. ensure you're able to hide all symbols and ensure that you can't pass C++ objects through the C API such that one instance of a standard type is accessible/visible outside the library.
4. ensure free'ing dynamic allocations happens within your library
5. ensuring all errors are caught within your library

This might work, but also note the result might not be great for binary size; consumers of your library will wind up with a copy of a c++ runtime that can't be shared with other c++ applications.