We know it's monotonic so it's good for deltas which is what I wanted anyway.Yes, that what I said, it's good for deltas.
This function with static sf::Clock also has a weird 'reference'This is just an example, the good thing with user written code is that you can decide what you do. For example, you could write a "timeElapsedSinceAppStartup" function if you needed to. And in any case, it's not as weird as being OS-dependant, undocumented and potentially different in future versions of SFML.
It's also only good for deltasYes, since that's what you wanted. But you wrote it, so the constraints on it (documentation, consistent behaviour, etc.) are a lot relaxed compared to the same thing put in a middleware.
And it's silly and cumbersomeYou want to measure delta times, which is exactly what sf::Clock does. I don't think it's silly or cumbersome.
I now either need to write it when I want a quick two printfs somewhere or keep it in some header I useSo as many useful things ;)
And it relies on sf::Clock not causing problems by being a static local (which it doesn't but other/GL classes will so suddenly if you want it you need to know what's okay to break the "don't make SFML classes static/global" rule with and what isn't).It's not constructed before main(), unless you call that function to initialize a global variable. So that rule doesn't apply here.