[RFC] OOP Components

considered/rfc-oop-fields.rst

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+- Feature Name: Standard OOP model
+- Start Date: May 5th 2020
+- RFC PR:
+- RFC Issue:
+
+Summary
+=======
+
+Motivation
+==========
+
+Guide-level explanation
+=======================
+
+Components declarations
+-----------------------
+
+A record and tagged record type can now have 2 declarative regions where fields
+can be declared:
+
+- the package public view
+- the package private view
+
+A public view that allows for additional fields to be declared is denoted by
+`with private` after its declaration. The private view of a record type can
+then be split between its own public and private sections:
+
+For example:
+
+.. code-block:: ada
+
+   package P is
+      type R is record
+         Pub : Integer;
+       end record
+       with private; -- There are more fields in the private view
+
+       type T is tagged record
+          Pub : Integer;
+       end record
+       with private; -- There are more fields in the private view
+
+   private
+
+      type R is record
+         Priv : Integer;
+      end record;
+
+       type T is tagged record
+         Priv : Integer;
+       end record;
+   end P;
+
+Visibilty rules of these fields are following the usual package-visibilty rules.
+
+It is possible to declare empty public or private views either with an empty `record end record` section, or the shorthands `null record` syntax.
+
+For example, all of the following type declarations are legal:
+
+.. code-block:: ada
+
+   package Legal is
+      type R1 is null record with private;  -- This syntax is supported for declaring an empty public view
+
+      type R2 is record
+         Pub : Integer;
+      end record
+      with private;
+
+      type R3 is record
+         null;
+      end record with private;  -- This record type has both public and private views empty
+
+      -- Same as R1, R2, R3 in tagged type forms
+
+      type T1 is tagged null record with private;
+
+      type T2 is tagged record
+         Pub : Integer;
+      end record
+      with private;
+
+      type T3 is tagged null record with private;
+
+   private
+
+      type R1 is record
+         Priv : Integer;
+      end record;
+
+      type R2 is record
+         null;
+      end record;
+
+      type R3 is null record;  -- This record type has both public and private views empty
+
+      type T1 is tagged record
+         Priv : Integer;
+      end record;
+
+      type T2 is tagged null record;
+
+      type T3 is tagged null record;
+
+   end Legal;
+
+As outlined in the example, it is legal to declare both public and private views as empty.
+
+Reference-level explanation
+===========================
+
+Rationale and alternatives
+==========================
+
+Drawbacks
+=========
+
+Prior art
+=========
+
+Unresolved questions
+====================
+
+Future possibilities
+====================
+