Re: Ada.Execution_Time

[Adam Beneschan <adam@irvine.com>]

On Dec 16, 9:24 am, BrianG <briang...@gmail.com> wrote:
> Simon Wright wrote:
> > BrianG <briang...@gmail.com> writes:
>
> >>> Arguably, CPU_Time is misnamed, because it is *not*
> >>> some sort of time type.
> >> Then the package is misnamed too - How is "Execution_Time" not a time?
>
> > A 'time type'
> > [http://www.adaic.com/resources/add_content/standards/05rm/html/RM-9-6...]
> > (6) can be used as the argument for a delay statement. Wouldn't make a
> > lot of sense for an execution time! (well, perhaps one could think of
> > some obscure use ...)
>
> (Actually for a delay_until.)  That paragraph seems to contradict the
> previous one which says "any nonlimited type".

No, not really.  The rule that says "any nonlimited type" is a Name
Resolution Rule.  Those rules control how the language resolves
possibly ambiguous statements.  It's important to realize that Name
Resolution Rules are not legality rules, and it's possible for
something to be illegal and still satisfy the Name Resolution Rules,
which means that a "possible interpretation" can still cause an
ambiguity even if it's illegal.  Example:

   type Int is new Integer;
   function Overloaded (N : Integer) return Integer;
   function Overloaded (N : Integer) return Character;

   X : Int := Int (Overloaded (5));

This last call to Overloaded is ambiguous (and therefore illegal) even
though one definition of Overloaded returns a Character which cannot
legally be converted to Int.  The type conversion from a Character-
returning function to Int still satisfies the Name Resolution Rules
(4.6(6)).  Moral: Don't look at Name Resolution Rules if you're trying
to figure out whether something is legal.  (Other than when trying to
figure out whether something is unambiguous.)

> Shouldn't (6) define
> Real_Time.Time since it's not Calendar.Time and isn't
> implementation-defined?  

It should probably say "language-defined or implementation-defined".
D.8(18) does say that Real_Time.Time is one of those "time types".

                                 -- Adam