Re: Iterable container as generic parameter

[Lionel Draghi <lionel.draghi@gmail.com>]

Le 26/01/2018 à 10:09, emmanuel... a écrit :
>> But I probably would just use your original spec and add the container type
>> and iterator function, something like:
>>
>> generic
>>     type Cursor is (<>);
>>     with function Image (C : Cursor) return String;
>>     type Container (<>) is private;
>>     with package Iterator_Interfaces is
>>       new Ada.Iterator_Interfaces (Cursor, others => <>);
>>     with function Iterator (C : Container) return
>> Iterator_Interfaces.Forward_Iterator'Class;
>> function List_Image return String;
>>
> 
> I think that's a good starting point.

Ok, I have something that works (https://github.com/LionelDraghi/List_Image).

Instantiating this is not as simple as I hoped, but not that much a nightmare :

   with List_Image;

   with Ada.Containers.Indefinite_Hashed_Sets;
   with Ada.Strings.Hash_Case_Insensitive;
   ...
      -- Example here with a set of identifier
      package Id_Sets is new Ada.Containers.Indefinite_Hashed_Sets
        (String, Ada.Strings.Hash_Case_Insensitive, "=");
      Id_Set : Id_Sets.Set;

      use Id_Sets;
      function Id_Set_Image is new List_Image.Image
           (Cursor      => Cursor,
            Image       => Element,
            Iterator_If => Set_Iterator_Interfaces,
            Container   => Set,
            Iterator    => Iterate,
            Style       => List_Image.Bracketed_List_Style);
      ...
      Id_Set.Insert ("Salt");
      Id_Set.Insert ("Pepper");
      Put_Line (Id_Set_Image (Id_Set));


It becomes slightly more complex for Containers that don't directly export an Iterate function returning Forward_Iterator'class (but Reversible_Iterator'class).
You need then to provide a simple function :

   function Iterate (L : List) return
     List_Iterator_Interfaces.Forward_Iterator'Class is 
       (Iterate (L));

The signature Style package is generally simple, and may be application wide, shared among all List_Image instantiation.

Any idea to simplify is welcome.

-- 
-- Lionel