simple code can't compiled, without clear compiler warning (not clear enough to me at least)

simple code can't compiled, without clear compiler warning (not clear enough to me at least)

[Mehdi Saada]

I am learning and training through the Aix en Provence Ada courses.
I coded for the first time things more substantial than reading or writing strings. Neither the specification or the body can compile, and I can't see why.

generic 
        type Element_type is (<>); 
        type Indice_type is (<>); 
        type Tableau_type is array (Indice_type range <>) of Element_type; 
package Tri_selection is 
        procedure tri (T: in out Tableau_type); 
end Tri_selection; 

$ gcc-6 -c tri_selection.ads 
cannot generate code for file tri_selection.ads (package spec) 
gnatmake: "tri_selection.ads" compilation error 

I thought specifications could be compiled separately ?

the body can't compiled either.
package body Tri_selection is 
   temp : Element_type; 
   procedure tri (T: in out Tableau_type) is 
       procedure Swap (T: in out Tableau_type; A, B : in out Element_type) is 
          temp: Element_type; 
       begin 
          temp := T(A); 
          T(A) := T(B); 
          T(B) := T(A); 
       end Swap; 
       temp: Indice_type; 
   begin 
       for I in Tableau_type'Range loop 
          for J in I..Tableau_type'Last loop 
             if T(J) < T(Tableau_type'Last) then temp := J; 
             end if; 
          end loop; 
          Swap (T,temp,Tableau_type'Last); 
       end loop; 
    end tri; 
end Tri_selection;

mehdi@debian:~/essai$ gnatmake tri_selection.adb 
gcc-6 -c tri_selection.adb 
tri_selection.adb:7:35: expected type "Indice_type" defined at tri_selection.ads:3 
tri_selection.adb:7:35: found type "Element_type" defined at tri_selection.ads:2 
tri_selection.adb:8:27: expected type "Indice_type" defined at tri_selection.ads:3 
tri_selection.adb:8:27: found type "Element_type" defined at tri_selection.ads:2 
tri_selection.adb:8:35: expected type "Indice_type" defined at tri_selection.ads:3 
tri_selection.adb:8:35: found type "Element_type" defined at tri_selection.ads:2 
tri_selection.adb:9:27: expected type "Indice_type" defined at tri_selection.ads:3 
tri_selection.adb:9:27: found type "Element_type" defined at tri_selection.ads:2 
tri_selection.adb:9:35: expected type "Indice_type" defined at tri_selection.ads:3 
tri_selection.adb:9:35: found type "Element_type" defined at tri_selection.ads:2 
tri_selection.adb:19:33: expected type "Element_type" defined at tri_selection.ads:2 
tri_selection.adb:19:33: found type "Indice_type" defined at tri_selection.ads:3 
gnatmake: "tri_selection.adb" compilation error 

Re: simple code can't compiled, without clear compiler warning (not clear enough to me at least)

[pascal.malaise]

Le mercredi 29 novembre 2017 16:17:03 UTC+1, Mehdi Saada a écrit :
> $ gcc-6 -c tri_selection.ads 
> cannot generate code for file tri_selection.ads (package spec) 
> gnatmake: "tri_selection.ads" compilation error 
> 
> I thought specifications could be compiled separately ?
In fact GNAT compiles the spec (no error in this case) but does not generate the code associated to it?

>           temp := T(A); 
T is an array, indexed by Indice_Type, of elements of type Element_Type.
Swap shall swap two elements of T knwowing the *indexes* of elements.
You should declare:
  procedure Swap (T: in out Tableau_type; I, J : in out Indice_Type)
and implement it and call it accordingly.

Re: simple code can't compiled, without clear compiler warning (not clear enough to me at least)

[A. Cervetti]

wednesday 29 november 2017 16:17:03 UTC+1, Mehdi Saada wrote:

> $ gcc-6 -c tri_selection.ads 
> cannot generate code for file tri_selection.ads (package spec) 
> gnatmake: "tri_selection.ads" compilation error 
> 
> I thought specifications could be compiled separately ?

Yes, they can, but for syntax check only. They cannot generate code (like explained in the message).

try: gcc-6 -gnats -c tri_selection.ads
> 
> the body can't compiled either.

> gcc-6 -c tri_selection.adb 
> tri_selection.adb:7:35: expected type "Indice_type" defined at tri_selection.ads:3 
> tri_selection.adb:7:35: found type "Element_type" defined at tri_selection.ads:2 
> tri_selection.adb:8:27: expected type "Indice_type" defined at tri_selection.ads:3 
> tri_selection.adb:8:27: found type "Element_type" defined at tri_selection.ads:2 
> tri_selection.adb:8:35: expected type "Indice_type" defined at tri_selection.ads:3 
> tri_selection.adb:8:35: found type "Element_type" defined at tri_selection.ads:2 
> tri_selection.adb:9:27: expected type "Indice_type" defined at tri_selection.ads:3 
> tri_selection.adb:9:27: found type "Element_type" defined at tri_selection.ads:2 
> tri_selection.adb:9:35: expected type "Indice_type" defined at tri_selection.ads:3 
> tri_selection.adb:9:35: found type "Element_type" defined at tri_selection.ads:2 
> tri_selection.adb:19:33: expected type "Element_type" defined at tri_selection.ads:2 
> tri_selection.adb:19:33: found type "Indice_type" defined at tri_selection.ads:3 
> gnatmake: "tri_selection.adb" compilation error

I think that the message are enough self explicative.
You defined the parameters A and B as Element_Type:
> procedure Swap (T: in out Tableau_type; A, B : in out Element_type)

than you used them as indexes:
>          temp := T(A);
>          T(A) := T(B);

the indexes should be Indice_type.

also you called Swap with the actual parameter temp and Tableau_type'Last
that are Index_type.

redefine Swap as
procedure Swap (T: in out Tableau_type; A, B : in out indice_type)

Now there are other errors, but I'll leave to you the pleasure of discovery.

A.

Re: simple code can't compiled, without clear compiler warning (not clear enough to me at least)

[Mehdi Saada]

Indeed, I found it. Now it works... I mean it compiled. Haven't use it in a actual program yet. I'm not used to going to the column number indicated.
But I could compile it both with Tableau_type'Last and T'Last. The manual says:
"The following attributes are defined for a prefix A that is of an array type (after any implicit dereference), or denotes a constrained array subtype"

That means I should rather put T'Last, since my generic formal type parameter for the Tabeau_type is unconstrained, so the library can't know if the provided subtype will or not be bound ?

Re: simple code can't compiled, without clear compiler warning (not clear enough to me at least)

[AdaMagica]

Am Mittwoch, 29. November 2017 18:27:56 UTC+1 schrieb Mehdi Saada:
> 
> That means I should rather put T'Last, since my generic formal type parameter for the Tabeau_type is unconstrained, so the library can't know if the provided subtype will or not be bound ?

That's correct.