Сreate attributes.

Сreate attributes.

[eduardsapotski]

Sorry for the stupid question...

For example. I have type:

   type Person is record
      First_Name : Unbounded_String := Null_Unbounded_String;
      Last_Name : Unbounded_String := Null_Unbounded_String;
   end record;

There is a list:

   package People_Package is new  Ada.Containers.Vectors(Natural, Person);
   People : People_Package.Vector;

Next, I want to display this list with headers:

----------------------------
|   NAME    |   SURNAME    |
----------------------------
|   John    |    Smith     |
|   Ada     |   Lovelace   |
...
----------------------------

Can I use attributes to display headers?
For example something like this:

People'First_Name_Header


How can this be implemented?

Re: Сreate attributes.

[Brad Moore]

On Friday, December 21, 2018 at 10:37:14 PM UTC-7, eduards...@gmail.com wrote:
> Sorry for the stupid question...
> 
> For example. I have type:
> 
>    type Person is record
>       First_Name : Unbounded_String := Null_Unbounded_String;
>       Last_Name : Unbounded_String := Null_Unbounded_String;
>    end record;
> 
> There is a list:
> 
>    package People_Package is new  Ada.Containers.Vectors(Natural, Person);
>    People : People_Package.Vector;
> 
> Next, I want to display this list with headers:
> 
> ----------------------------
> |   NAME    |   SURNAME    |
> ----------------------------
> |   John    |    Smith     |
> |   Ada     |   Lovelace   |
> ...
> ----------------------------
> 
> Can I use attributes to display headers?
> For example something like this:
> 
> People'First_Name_Header
> 
> 
> How can this be implemented?

You could use a class-wide type or a type with discriminants such as;

   type Person_Attribute_Kinds is (Name, Surname);
   
   type Person_Attribute (Attribute_Name : Person_Attribute_Kinds
                          := Person_Attribute_Kinds'First) is
      record
         case Attribute_Name is
            when Name | Surname =>
               Name_String : Unbounded_String := Null_Unbounded_String;
         end case;
      end record;
      
      type Person is
         record
            First_Name : Person_Attribute(Name);
            Last_Name  : Person_Attribute(Surname);
         end record;
      
   X : Person;
begin
   Put_Line ("| " & X.First_Name.Attribute_Name'Image &
              " | " & X.Last_Name.Attribute_Name'Image & " |");

Re: Сreate attributes.

[eduardsapotski]

Thank!

Re: Сreate attributes.

[Brad Moore]

On Friday, December 28, 2018 at 2:26:04 AM UTC-7, eduards...@gmail.com wrote:
> Thank!

You're welcome!

I think a slight improvement would be to make the Person_Attribute type non-mutable (i.e. remove the ":= Person_Attribute_Kinds'First" on the Attribute_Name discriminant), since I presume you'd want to constrain the First_Name component of the Person type to always be a Name, and constrain the Last_Name component to always be a Surname. In other words, you dont want to allow someone to assign a Surname to the First_Name, or a First_Name value to the Last_Name.

Brad