Re: exception parameters

[Stephen Leake <stephen_leake@acm.org>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

> A database connection type may have a primitive operation Get_Last_Error. So
> when you catch Database_Error and the connection object is still here (why
> should it disappear?), you can get a detailed error description from it.
> Get_Last_Error could be made task unique, if connection object will be used
> concurrently.

Yes, you _could_ do it that way. But embedding the information in the
exception message is better; there are no global variables involved,
so there are no tasking issues. It would be even better if you could
embed a type other than string, but that's not as much gain.

> > I understand there are lots of difficult implementation issues
> > with general exception parameters, and it can certainly be carried
> > too far.
> > 
> > Ada allows one string parameter for exceptions. If it also allowed one
> > integer parameter, that might be a nice compromise :).
> 
> But the exception is already a sort of number. Why not to allow ranges?
> 
> Connection_Lost_Error, SQL_Syntax_Error, Unknown_DB_Error : exception;
>    -- A consequent set of exceptions
> Database_Error renames range Connection_Lost_Error..Unknown_DB_Error;
> 
> or
> 
> subtype Database_Error is range Connection_Lost_Error..Unknown_DB_Error;
>    -- A range of exceptions

An actual 64 bit number encodes much more information.

-- 
-- Stephe