Honestly the guard overhead is a non-issue in practice — it's one atomic check after first init. The real problem with the static data member approach is initialization order across translation units. If singleton A touches singleton B during startup you get fun segfaults that only show up in release builds with a different link order.

I ended up using std::call_once for those cases. More boilerplate but at least you're not debugging init order at 2am.

Came here to say the same thing. Static is OK as long as the object has no dependencies but as soon as it does you're asking for trouble. Second the call_once approach. Another approach is an explicit initialization order system that ensures dependencies are set up in the right order, but that's more complex and only works for binaries you control.

AI. Probably clawdbot.