Xcode 10 call to unavailable function std::visit

Question

When compiling following program with Xcode 10 GM:

#include 
#include 
#include 

void hello(int) {
    std::cou         


        

Answer 1

This happens because std::visit throws an bad_variant_access exception in cases described here and since the implementation of that exception depends on an newer version of libc++ you are required to use versions of iOS and macOS that ship this new version (macOS 10.14 and iOS 12).

Thankfuly, there is a implementation path available for when c++ exceptions are turned off which doesn't depend on the newer libc++ so if possible you can use that option.

P.S. About the case where you increased the minimum deployment target to 10.14 and were still able to run the program normally on 10.13 I'm guessing you would run into problems at the point that this new exception would be triggered (since the exception method which relies on a newer version of libc++ would not be resolved).