@jwakely, @CaseyCarter: LWG perspectives welcome!

Tentatively, what would the rule for using struct be?

• not having private members
• being an aggregate
• not having (non-special) member functions
• ...?

There are a ton of structs in Ranges, which I think is a consequence of the fact that Eric Niebler and I both prefer struct to class in our personal styles, and not the result of any explicit particular style choice on the part of LEWG or LWG. We wrote struct because that's what the implementations said, and nobody ever thought it important enough to ask me to change it.

I think Library generally uses the rule that structs have no private data members whereas classes have at least one and maintain invariants, but I wouldn't be surprised if Ranges wasn't the only violator of this rule.

"No private members" is certainly a good first step. For purposes of the standard, some classes don't have any visible members, but they are containers or so and thus must have data members; they're just not shown. Those should be "class" as well.

Editorial meeting opinion: This is not overly important, but we can certainly create and write down a rule. Based on the above, it should be something like "If it has invariants, it's a class, otherwise a struct".

Added a wiki entry that recomends the above rule. No further action at this point, though cleanup PRs are welcome.