Re: Discriminants constraining unconstrained array types

[Jeffrey Carter <jrcarter@acm.org>]

James Rogers wrote:
> 
> Matthew Woodcraft wrote:
> >
> > The following rule appears in the GNAT coding style guide:
> >
> > | Do not declare discriminated record types where the discriminant is
> > | used for constraining an unconstrained array type. (Discriminated
> > | records for a variant part are allowed.)
> >
> The first problems is memory usage. Take the following example:
> 
> type Unconstrained_Type is array(Positive range <>) of Integer;
> 
> type Inadvised_Record_Type (Max : Positive) is record
>    Buffer : Unconstrained_Type(1..Max);
> end record;

I am not aware of any compilers that generate unreasonable code for such
a construct. They all size objects of such a type based on the actual
subtype. A memory problem frequently occurs if the type has a default
discriminant and unconstrained objects are created, but the rule goes
beyond excluding such types/objects.

-- 
Jeff Carter
"Perfidious English mouse-dropping hoarders."
Monty Python & the Holy Grail