Re: Question about out parameters of unconstrained array type.

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

On 02/26/2012 05:25 AM, Alexander Senier wrote:
>
> Can anybody comment on the legality of using attributes of an out parameter of
> an unconstrained (array) type in Ada? A brief skim through LRM could not
> enlighten me...

ARM-83 6.2 (Formal Parameter Modes) has:

out      The  formal  parameter is a variable  and permits updating of the
           value of the associated actual parameter.

           The value  of  a scalar parameter that is not updated by the call
           is undefined  upon return;  the  same  holds for the  value  of a
           scalar subcomponent,  other  than a  discriminant.   Reading  the
           bounds and discriminants  of the  formal  parameter  and  of  its
           subcomponents is allowed,  but no other reading.

This explicitly allows reading the bounds of a mode-out formal array parameter 
(note that, in Ada 83, you could not read the value of a mode-out parameter, 
even after assigning to it). ARM-95 and later are more formal, and lack such a 
simple statement about reading attributes.

Whether 'Length counts as "bounds" is another matter; 'Length is 'Pos ('Last) - 
'Pos ('First) + 1, so I'd think it does.

-- 
Jeff Carter
"If you think you got a nasty taunting this time,
you ain't heard nothing yet!"
Monty Python and the Holy Grail
23

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