Re: Unconstrained Arrays

[sjw <simon.j.wright@mac.com>]

On Mar 20, 1:53 am, "Peter C. Chapin" <pcc482...@gmail.com> wrote:
> belteshazzar <gbelteshaz...@gmail.com> wrote innews:386b0e00-a1c6-4c5f-adf7-89b8543d0e2d@c11g2000yqj.googlegroups.com:
>
> > Unfortuantely this is an optimisation and actually doesn't occur with
> > optimisation off. (I just ran a test program). I'm told that due to
> > the significant performance hit of the array initialisers when
> > optimisation is turned off we can't use that.
>
> Are those initializers actually necessary?
>
> type Unconstrained_Array is array(Integer range <>) of Integer;
>
> My_Array : Unconstrained_Array(-10_000 .. 10_000);
>
> In the above the array is uninitialized. Yes, you have to provide
> constraints, but you don't have to initialize the array here (obviously
> you'll need to do so eventually... perhaps as part of your algorithm). The
> code you showed use an array aggregate to initialize the array... the
> constraints where taken from the initializer. However, there are other ways
> to specify the constraints.

There is a deep language-lawyerly reason (which I don't understand)
why an array like your My_Array can't be aliased (at any rate in
Ada95); you have to use the initialize-with-aggregate approach.
Perhaps that's what leads to the initialize-with-aggregate style.