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+--  Type interning - set of unique objects.
+--  Copyright (C) 2019 Tristan Gingold
+--
+--  GHDL is free software; you can redistribute it and/or modify it under
+--  the terms of the GNU General Public License as published by the Free
+--  Software Foundation; either version 2, or (at your option) any later
+--  version.
+--
+--  GHDL is distributed in the hope that it will be useful, but WITHOUT ANY
+--  WARRANTY; without even the implied warranty of MERCHANTABILITY or
+--  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+--  for more details.
+--
+--  You should have received a copy of the GNU General Public License
+--  along with GHDL; see the file COPYING.  If not, write to the Free
+--  Software Foundation, 59 Temple Place - Suite 330, Boston, MA
+--  02111-1307, USA.
+
+with Types; use Types;
+with Hash; use Hash;
+
+--  This generic package provides a factory to build unique objects.
+--  Get will return an existing object or create a new one.
+generic
+   --  Parameters of the object to be created.
+   type Params_Type (<>) is private;
+
+   --  Object to be built and stored.
+   type Object_Type is private;
+
+   --  Reduce PARAMS to a small value.
+   --  The required property is: Hash(P1) /= Hash(P2) => P1 /= P2.
+   with function Hash (Params : Params_Type) return Hash_Value_Type;
+
+   --  Create an object from PARAMS.
+   with function Build (Params : Params_Type) return Object_Type;
+
+   --  Return True iff OBJ is the object corresponding to PARAMS.
+   with function Equal (Obj : Object_Type; Params : Params_Type)
+                       return Boolean;
+package Interning is
+   --  Initialize.  Required before any other operation.
+   procedure Init;
+
+   --  If there is already an existing object for PARAMS, return it.
+   --  Otherwise create it.
+   function Get (Params : Params_Type) return Object_Type;
+
+   type Index_Type is new Uns32;
+   No_Index : constant Index_Type := 0;
+   First_Index : constant Index_Type := 1;
+
+   --  Get the number of elements in the table.
+   function Last_Index return Index_Type;
+
+   --  Get an element by index.  The index has no real meaning, but the
+   --  current implementation allocates index incrementally.
+   function Get_By_Index (Index : Index_Type) return Object_Type;
+end Interning;