Native C++ references are technically unsafe, so code that uses them would not qualify as "strict" SaferCPlusPlus code. In the case of your example, the "double&" is technically not kosher. The easiest way to make it safe would probably be to use a (safe) iterator instead of a native reference. So instead of
double& dangling = data[0];
you could make it
auto not_dangling_iter = data.begin();
// not_dangling_iter += 0;
C++ references are the one unsafe element that does not have a "compatible" safe replacement. Unfortunately, you have to convert your references to pointers (or iterators). I don't think there is a way to create a "safe" reference with an interface compatible with native references. Apparently C++ will at some point add the ability to overload the dot operator, but I'm not sure that will be enough to be able to emulate C++ references.
And while I can overload the & (address of) operator to "prevent" you from getting a native pointer to a "safe" object, I don't know if there's a way to prevent you from getting a native reference. If you wanted to somehow enforce a prohibition on the use of unsafe C++ elements (like references), that would probably require some sort of static tool that is not yet available. But should be fairly straightforward to implement, I think.
But if you just want some confidence in the safety of the code you write, it doesn't take much effort to reliably avoid using C++'s unsafe elements.
And while I can overload the & (address of) operator to "prevent" you from getting a native pointer to a "safe" object, I don't know if there's a way to prevent you from getting a native reference. If you wanted to somehow enforce a prohibition on the use of unsafe C++ elements (like references), that would probably require some sort of static tool that is not yet available. But should be fairly straightforward to implement, I think.
But if you just want some confidence in the safety of the code you write, it doesn't take much effort to reliably avoid using C++'s unsafe elements.