Re: Missing Index Value in Array Aggregate

["Randy Brukardt" <randy@rrsoftware.com>]

"Adam Beneschan" <adam@irvine.com> wrote in message
news:1190822071.488118.316450@y42g2000hsy.googlegroups.com...
...
> Note, though, that array *types* don't have bounds on their indexes.
> An array subtype is an array type plus (possibly) a constraint, where
> the constraint puts bounds on the indexes.  Once the type of the above
> aggregate is determined, the aggregate will have an (unnamed) subtype
> of that type with a constraint of (2..4).  Then, depending on what you
> do with that aggregate, the subtype will be *converted* to some other
> subtype.  If you declare an object:
>
>    type int4 is array(1..4) of integer;
>    A : int4 := (2 => 1010, 3 => 2020, 4 => 3030);

To expand on this a bit, in Ada 95, array bounds "slide" on assignment -
only the length of the array matters. So the bounds given in the aggregate
are not necessarily meaningful. The assignment

    type int3 is array(1..3) of integer;
    A : int3 := (2 => 1010, 3 => 2020, 4 => 3030);

is legal and does not raise Constraint_Error. Thus the number of cases where
you could tell statically that the aggregate is wrong is fairly few. There
are some, though; if the index values aren't continguous, the aggregate is
illegal:

    type int3 is array(1..3) of integer;
    A : int3 := (1 => 1010, 3 => 2020, 4 => 3030); -- Illegal.

And, as Adam points out, I'm not aware of any Ada compiler that doesn't put
out a warning when it knows an exception is going to be raised. Don't turn
off (or ignore) all warnings!

                                Randy.