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