From: Peter Dimov (pdimov_at_[hidden])
Date: 2004-06-29 09:41:09
Michael Glassford wrote:
> Doug Gregor wrote:
>
>> Refinements of a concept can only add restrictions,
>> they cannot remove them.
>
> True. But it's not hard to define the concepts in such a way that the
> lock classes can have different constructors:
>
> Lock concept defines all lock operations except constructors.
> TryLock concept refines Lock by adding try_* methods.
> TimedLock concept refines TryLock by adding timed_* methods.
>
> ScopedLock refines Lock by adding appropriate constructors.
> ScopedTryLock refines TryLock by adding appropriate constructors.
> ScopedTimedLock refines TimedLock by adding appropriate constructors.
Yes, it's possible to define them, but it'd be pointless to do so. The idea
of a concept X that refines concept Y is that a generic function can use a X
as if it were an Y. In this case, all refinements are wasted because
construction is a very important property of the concept, since the typical
usage pattern creates scoped locks locally, instead of receiving them
already constructed.