Re: Allocation questions

[Adam Beneschan <adam@irvine.com>]

On May 28, 6:39 am, Martin <martin.do...@btopenworld.com> wrote:
> > 2 more questions:
>
> > 1) In fact (due to my background!), I would like to use the dot notation:
> > object.method.
> > So I have add "tagged":

I'm not sure I'd recommend declaring a type "tagged" JUST to get the
dot notation.  There's a small amount of overhead involved with making
a type tagged; but more importantly, a fair number of language rules
are different for tagged types than for untagged types.  (You ran into
one different rule below; another one that comes to mind immediately
is that there are differences in the semantics of "=".  There are
others.  You might not run into any of them, though.)


> >      type Delay_Type (Size : Nb_Of_Samples := 0) is tagged private;
> >      ...
> > private
> >      type Delay_Type (Size : Nb_Of_Samples :=0) is tagged record
> >       ...
>
> > When I compile, I have:
> > "discriminants of tagged type cannot have defaults"
> > How can I fix it ?
>
> Just remove the " := 0" bit.

To elaborate, the main advantage of using the default is that after
you declare an object of type Delay_Type, you can change its Size by
reassigning the whole object.  If you don't need to use this feature---
i.e. if you will declare an object of type Delay_Type(Size=>N) and
then never change the Size of that object afterwards---then I don't
think there's any need to use the default.


> > 2) If Nb_Of_Samples range is too large, around 1..5_000_000, I have a
> > nice Segmentation fault. How can I fix that ?

As Xavier pointed out, using a default could cause a lot larger array
to be allocated (because the Size could be changed later).  If you
remove the default, this problem may go away on its own.  I don't see
how an array of five million floats would cause a problem.  (Not these
days, anyway.  Back when I used to work on a mainframe that took up a
whole room and had a whopping ONE MEGABYTE of RAM, maybe it would have
been a problem.  I also used to put my COBOL programs on punch cards
and walk five miles to school, uphill both ways...)

                                  -- Adam