------------------------------------------------------------------------------
-- XML/Ada - An XML suite for Ada95 --
-- --
-- Copyright (C) 2007-2017, AdaCore --
-- --
-- This library is free software; you can redistribute it and/or modify it --
-- under terms of the GNU General Public License as published by the Free --
-- Software Foundation; either version 3, or (at your option) any later --
-- version. This library is distributed in the hope that it will be useful, --
-- but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHAN- --
-- TABILITY or FITNESS FOR A PARTICULAR PURPOSE. --
-- --
-- As a special exception under Section 7 of GPL version 3, you are granted --
-- additional permissions described in the GCC Runtime Library Exception, --
-- version 3.1, as published by the Free Software Foundation. --
-- --
-- You should have received a copy of the GNU General Public License and --
-- a copy of the GCC Runtime Library Exception along with this program; --
-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
-- <http://www.gnu.org/licenses/>. --
-- --
------------------------------------------------------------------------------
-- This package provides smart pointers, ie types that encapsulate a
-- standard pointer and provide automatic memory management for it.
with Ada.Finalization;
with Interfaces;
package Sax.Pointers is
-- All types that can be encapsulated in a smart pointer must derive from
-- a common ancestor, which adds a Refcount field to them. The advantage is
-- that we require one less memory allocation *per pointer*, since
-- encapsulating any type requires that the pointer is defined as
-- type Pointed_Data is record
-- Data : access Encapsulated;
-- Refcount : Natural := 1;
-- end record;
-- type Pointer is new Ada.Finalization.Controlled with record
-- Data : access Pointed_Data;
-- end record;
-- and the association with the refcount is less tight
--
-- On the other hand, the implementation chosen in this package requires
-- the encapsulated type to be slightly bigger, since it includes the tag.
-- But on the whole, memory usage is the same, with one less alloc/free, so
-- more efficient.
type Root_Encapsulated is abstract tagged private;
type Root_Encapsulated_Access is access all Root_Encapsulated'Class;
procedure Free (Data : in out Root_Encapsulated);
-- Free the memory associated with Data.
-- By default, it does nothing
generic
type Encapsulated is abstract new Root_Encapsulated with private;
package Smart_Pointers is
type Pointer is private;
Null_Pointer : constant Pointer;
type Encapsulated_Access is access all Encapsulated'Class;
function Allocate (Data : Encapsulated'Class) return Pointer;
function Allocate (Data : access Encapsulated'Class) return Pointer;
pragma Inline (Allocate);
-- Allocate a new pointer.
-- Data is adopted by the smart pointer, and should no longer be
-- referenced directly elsewhere. This is meant for efficiency in cases
-- where copying the data would cost too much.
-- Typical code looks like:
-- Tmp := new Encapsulated;
-- Ptr := Allocate (Tmp);
-- (You can't do Allocate(new Encapsulated) for visibility reasons)
function Get (P : Pointer) return Encapsulated_Access;
pragma Inline (Get);
-- Return the data pointed to by P
function "=" (P1, P2 : Pointer) return Boolean;
-- Whether the two pointers point to the same data
private
type Pointer is new Ada.Finalization.Controlled with record
Data : Root_Encapsulated_Access;
end record;
procedure Finalize (P : in out Pointer);
procedure Adjust (P : in out Pointer);
-- Take care of reference counting
Null_Pointer : constant Pointer :=
(Ada.Finalization.Controlled with Data => null);
end Smart_Pointers;
private
type Root_Encapsulated is abstract tagged record
Refcount : aliased Interfaces.Integer_32 := 1;
end record;
end Sax.Pointers;