Re: Structured exception information

[Jeffrey Carter <spam.jrcarter.not@spam.acm.not.org>]

Dmitry A. Kazakov wrote:
> 
>    procedure Foo raises Foo_Error; -- Compile error!

Generally, subprograms should raise exceptions because of precondition 
violations. If the preconditions are met, the subprogram should not 
raise an exception (barring things that are beyond the developer's 
control, such as running out of memory). So it would be better to 
associate a subprogram with a list of preconditions with the exception 
raised if each is violated:

function Arccoth (Coth : Real) return Real
when abs Coth < 1.0 raise Invalid_Coth;

procedure Time_Limited (X : in Integer)
when X = 0 raise Zero_X and
when Ada.Calendar.Clock >=
      Ada.Calendar.Time_Of (Year    => 2010,
                            Month   => 1,
                            Day     => 1,
                            Seconds => 0.0)
raise Too_Late;