"it's one atomic check after first init" And that's slow :P [0] If you don't need to access it from multiple threads, cutting that out can mean a huge differenc

"it's one atomic check after first init" And that's slow :P [0] If you don't need to access it from multiple threads, cutting that out can mean a huge difference in a hot path. [0] https://stackoverflow.com/questions/51846894/what-is-the-performance-of-stdatomic-vs-non-atomic-variables https://stackoverflow.com/questions/51846894/what-is-the-per...