> There certainly are problems for which ABI stability might be important. Like when you're a library, as FoundationDB is. C and C++ have a specific approach

> There certainly are problems for which ABI stability might be important. Like when you're a library, as FoundationDB is. C and C++ have a specific approach to ABI stability that induces a specific kind of misery (more generally the ABI is fragile), but Swift is ABI stable without that misery. If the first thing you need to do to in order to be a library is lose all your language safety features by marshaling to and from C/C++ to create the actual API, even when both sides of the API are in the same language that's just a sad waste.