Re: "unconstrained subtype in component declaration" vs "discriminant in constraint must appear alone"

[Shark8 <onewingedshark@gmail.com>]

On Tuesday, February 23, 2021 at 3:06:19 PM UTC-7, 0012... wrote:
> Please help figure out this: 
> 
> type CARDS is new cards_numbers range 1..52; 
> --> 
> 41:10 missing case values: -128 .. 0 
> 41:10 missing case values: 5 .. 127 
> 41:25 subtype of expression is not static, alternatives must cover base type 
> from --> 
> [card in CARDS, of course] 
> case (card / 13) +1 is 
> when 1 => put("Spades"); 
> when 2 =>put("Hearts"); 
> when 3 =>put("Spades"); 
> when 4 =>put("Clovers"); 
> end case; 

Hm, I would recommend using an enumeration here.
Type Suit is (Spades, Hearts, Clubs, Diamonds); -- Or whatever you have/terms you want.
Function Get_Suit( Card : Cards ) return Suit is
    ( Suit'Val( Natural(Card)/13 ) );

Then use:
Case Get_Suit(card) is
  When Diamonds => ...
  When Hearts => ...
  When Spades => ...
  When Clubs => ...
End case;

> 
> how can the compiler not know that CARD is limited from 1 to 52, including 0 for the base type (type Cards_numbers is range 0..52) 
> 
> also what's wrong here: 
> Context => 
> type Sets_of_Card is array (Nombre_cartes range <>) of Cards;
> type CARDS_SETS (Nb: Nombre_cartes := 0) is record 
> Set: Sets_of_Card (1..Nb) := INITIALIZATION (Nb); 
> end record;
> pack.nb = 5 
> pack.set'last = 5 
> faulty line: 
> PACK := (pack.nb-1, Pack.Set(pack.set'First..Pack.Nb-1)); 
> issue: 
> raised CONSTRAINT_ERROR : discriminant check failed 
If you have something like PACK : CARD_SETS(7):= [...], then you cannot have a CARD_SETS(4) assigned to it.
Likewise, if you have a PACK : CARD_SETS := (Nb => 3, [proper-set-of-cards]), you cannot assign a (Nb => 2, [proper-set-of-cards]) to it, because to do so would be to alter the discriminant.

Now, one thing that you may not be cognizant of is that Sets_of_Cards is a full deck* of cards, so CARDS_SET(3) is three decks of cards.
* -- But this isn't quite true, you could set the full range of the array to a single value, say 4.

A bit of advice: Ada is really good at describing the problem-space using the type-system, so don't try to force the problem-space into some other domain.
There is nothing wrong with saying
Type Suit is (Hearts, Clubs, Diamonds, Spades);
Type Color is (Red, Black);
Function Is_Red(Item : Suit) return Boolean is ( Color'Val(Suit'Pos(Item) mod 2) );
Type Rank is ('1','2','3','4','5','6','7','8','9','0','J','Q','K','A'); -- Or numbers, card-ranking is kinda "squishy".
Type Card is record
  My_Suit : Suit;
  My_Rank : Rank;
end type;
Function "<"(Left, Right: Card) return Boolean is --Ranking mechanism.
--...

> and why is this expression not rejected: 
> Pack := (pack.nb+1, pack.set & Card); 
> while this one is rejected ? 
I believe it's because you're trying to re-set the discriminant; without a suitable example it's hard to tell though.

> Pack := (pack.nb+1, pack.set & CARDS_SET'(1=> Card)); 
> a95cop1.adb:126:39: invalid operand types for operator "&" 
> this works but overkill... -> Pack := (pack.nb+1, (pack.set with delta PACK.NB+1 => Card));
Yeah, here you're straight-up trying to overwrite the discriminant.