[SOLVED] In ada programming language, Is there a way to create a subtype which takes differently positioned enums of a type?

In ada programming language, Is there a way to create a subtype which takes differently positioned enums of a type?

I am trying create a subtype which takes certain enumerations of a type for example,

type Integers_Type is (1,2,3,4,5,6,7,8,9,10);

I want something like this,

subtype Odd_Numbers_Type is Integers_Type (1,3,5,7,9);

I understand that when we use the keyword subtype of a type we need to use range, but the problem is the enumeration is not in a series.

Solution

For this kind of values filtering, I would use subtype predicates.

In your case, modifying your enumeration according to what Keith said :

type Integers_Type is (ONE,TWO,THREE,FOUR,FIVE,SIX,SEVEN,EIGHT,NINE,TEN);

subtype Odd_Numbers_Type is Integers_Type 
   with Static_Predicate => Odd_Numbers_Type in ONE | THREE | FIVE | SEVEN | NINE;

If you want to use numeric types instead of enumeration, use the following

type Integers_Type is range 1 .. 10;

subtype Odd_Numbers_Type is Integers_Type
   with Dynamic_Predicate => Odd_Numbers_Type mod 2 /= 0;

For more information, you can read the rationale

EDIT :

For Enumeration types, the following compiles using gnatmake -gnata -gnatVa test_enum.adb but warns about the affectation line 14 and fails at execution because of the assert linked to the static predicate.

with Ada.Text_IO; use Ada.Text_IO;

Procedure Test_Enum is
   type Integers_Type is (ONE,TWO,THREE,FOUR,FIVE,SIX,SEVEN,EIGHT,NINE,TEN);

   subtype Odd_Numbers_Type is Integers_Type 
     with Static_Predicate => Odd_Numbers_Type in ONE | THREE | FIVE | SEVEN | NINE;
   
   Test_I : Integers_Type := TWO;
   Test_O : Odd_Numbers_Type := ONE;
begin
   Put_Line("Test_I=" & Integers_Type'Image (Test_I));
   Put_Line ("Test_O=" & Odd_Numbers_Type'Image (Test_O));
   Test_O := Test_I;
   Put_Line ("Test_O=" & Odd_Numbers_Type'Image (Test_O));
end Test_Enum;

For integer types, using the gnatmake -gnata -gnatVa test_int.adb compilation command, the compiler warns that the check will fail at runtime which is the case as the assertion is triggered.

with Ada.Text_IO; use Ada.Text_IO;

Procedure Test_Int is
   type Integers_Type is range 1 .. 10;

   subtype Odd_Numbers_Type is Integers_Type
     with Dynamic_Predicate => Odd_Numbers_Type mod 2 /= 0;
   
   Test_I : Integers_Type := 2;
   Test_O : Odd_Numbers_Type := 1;
begin
   Put_Line("Test_I=" & Integers_Type'Image (Test_I));
   Put_Line ("Test_O=" & Odd_Numbers_Type'Image (Test_O));
   Test_O := Test_I;
   Put_Line ("Test_O=" & Odd_Numbers_Type'Image (Test_O));
end Test_Int;

In both cases, removing the -gnata flag will make the program working without taking care of the predicate as asserts are desactivated.