Re: New to Ada, why these warning messages?

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

Botton explained the warnings you got, but a larger issue is that this is poor
Ada and so not the best thing to be learning from.

On 12/31/2015 07:19 PM, Dale Dellutri wrote:
> 
>    -- Some Paint arrays.  The first one is initialized with a list
>    -- of colors.
>    A: AType := (Red, Red, Pink, Blue, Orange, Cherry, Indigo, Indigo);

This is not a list. It's a positional array aggregate.

>    I: Integer;          -- Loop index.

As you've discovered, this is not the loop index. Loop indices are declared by
the loop, are constant within the loop, and cease to exist when the loop is
exited. Whoever wrote this was probably used to languages in which you had to
declare a loop index like this, and hadn't learned how Ada works.

>    -- Use positions to set varioius values in various places.
>    B := (5 => Green, 2 => Orange, 6..8 => Indigo, 1|3|4 => Brown);

This is a named array aggregate.

>    -- Set the entire array to Blue.
>    C := (AType'First .. AType'Last => Blue);

This would be better written

   (Atype'range => Blue)

or

   (Paint => Blue)

>    -- Print the position numbers, spaced out to align with the
>    -- the printouts of each of the arrays below.
>    for I in 1..N loop

I would probably use

   for I in Atype'range loop

to avoid using a "magic number", even in a case like this in which it's unlikely
that a change to the constant won't also result in a change to the array range.

>    -- Print out the contents of each of A, B, and C.
>    for I in 1..N loop

   for I in A'range loop

>       Put(PNames(A(I)) & " ");
> 
>    for I in 1..N loop

   for I in B'range loop

>       Put(PNames(B(I)) & " ");
> 
>    for I in 1..N loop

   for I in C'range loop

>       Put(PNames(C(I)) & " ");

Tying the loop index to the array using 'range makes it easier for the compiler
to optimize away bounds checks.

-- 
Jeff Carter
"Strange women lying in ponds distributing swords
is no basis for a system of government."
Monty Python & the Holy Grail
66