alt Hacker News> If you aren't instantiating a template, then it isn't used, so who cares if it has theoretical errors to be figured out later?
Just because you aren't instantiating a template a particular way doesn't necessarily mean no one is instantiating a template a particular way.
A big concern here would be accidentally depending on something that isn't declared in the concept, which can result in a downstream consumer who otherwise satisfies the concept being unable to use the template. You also don't get nicer error messages in these cases since as far as concepts are concerned nothing is wrong.
It's a tradeoff, as usual. You get more flexibility but get fewer guarantees in return.
Of course what you are describing is possible, but those scenarios seem contrived to me. If you have reasonable designs I think they are unlikely to come up.
>Just because you aren't instantiating a template a particular way doesn't necessarily mean no one is instantiating a template a particular way.
What I meant is, if the thing is not instantiated then it is not used. Whoever does come up with a unique instantiation could find new bugs, but I don't see a way to avoid that. Likewise someone could just superficially meet the concept requirements to make it compile, and not actually implement the things they ought to. But that's not a problem with the language.