Re: syntaxic exploration

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 17-12-22 22:25 , Mehdi Saada wrote:
> How about that, then:
> return RES: T_POLYNOME :=
> 	T_DEGRE'MAX(POLY_A.DEGRE,POLY_B.DEGRE),(0..POLY_A.COEF'Last => POLY_A.COEF, others => Nulle)) do
> It says "p_poly_v1_g.adb:63:51: dynamic or empty choice in aggregate must be the only choice"

(You have omitted the opening '(', after the ":=".)

Yes, the range 0..POLY_A.COEF'Last is dynamic, so the error message is 
valid.

Moreover, here, too, the expression after the index range should be a 
T_RATIONNEL, not an array like POLY_A.COEF. The semantics of an 
association A .. B => X, in an array aggregate, is to give the same 
value, X, to all elements in the index range A .. B, so it is _not_ what 
you want to do here.

> I would like to write this (POLY_A.COEF'Range => POLY_A.COEF, others => Nulle)

That is equivalent, and should give you the same error, and also be 
wrong in the same way.

> but I know "POLY_A.COEF'Range =>" must be followed by a value
> of T_RATIONNEL, not a slice.

The same is true for "0..POLY_A.COEF'Last =>".

> But I don't know how to write "PUT POLY_A.COEF there, and as much
> Nulle as needed to fill the void if by chance POLY_B.DEGRE > POLY_A.DEGRE"

If you insist on using an aggregate to initialise RES, you could use 
this form, with array concatenation ("&" operator) for the COEF component:

    return RES : T_POLYNOME :=
      (T_DEGRE'MAX (POLY_A.DEGRE, POLY_B.DEGRE),
         POLY_A.COEF
       & (1 .. Xxx'MAX (0, POLY_B.DEGRE - POLY_A.DEGRE) => Nulle));

where Xxx is the index type of the COEF array (I forget its name).

However, I would do it differently; I would declare RES with just its 
discriminant:

    return
       RES : T_POLYNOME (T_DEGRE'MAX (POLY_A.DEGRE, POLY_B.DEGRE))
    do
       -- Assign values to RES.COEF using loops, something like:

       for C in RES.COEF'Range loop
          RES.COEF(C) :=
              (if C in POLY_A.COEF'Range then POLY_A.COEF(C) else 0)
            + (if C in POLY_B.COEF'Range then POLY_B.COEF(C) else 0);
       end loop;
    end return;

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
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