Broken?

[Sean Kelly]

And for the record, I'm absolutely pedantic about adding "final"
qualifiers to functions that aren't intended to be overridable,
and yet it recently came to light that the methods a class in
Druntime that I created (Condition) are not labeled final.  I
can't imagine any reason why I'd have made that decision
explicitly, since there's no real function to having them be
overridable.  It was obviously a mistake on my part, and yet
there are two instances where Condition has been subclassed and
these methods overridden (once by me, to be honest), to
questionable ends.  And so at this point I can't add the "final"
qualifier without breaking user code, even though it was always
meant to be there.

In short, I don't think that saying this is often overlooked is
even necessarily an assertion that library writers are sloppy or
don't care about performance.  It being the default behavior and
having no detectable issues at design time means that these
problems will slip in from time to time.  It's hard to grep for
the lack of a keyword.