You're going to need to bias in one direction or another. If you can safely inline assumptions regarding the int into the hot path that exists, with a consciously slower bail-out path if it's not an integer. Now consider a situation where `x` is probably an integer--but can be a string or null. We're rapidly getting to a situation where this is going to be puffy code that is hard to constrain to an effective hot path without running the code, yeah?

Profile-guided optimization seeks to do this for compiled languages like C++, but you also have a boatload more data to do it with. And, y'know. You're profiling the application. You're running it.