------------------------------------------------------------------------------
-- Copyright (c) 2013, Natacha Porté --
-- --
-- Permission to use, copy, modify, and distribute this software for any --
-- purpose with or without fee is hereby granted, provided that the above --
-- copyright notice and this permission notice appear in all copies. --
-- --
-- THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES --
-- WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF --
-- MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR --
-- ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES --
-- WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN --
-- ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF --
-- OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. --
------------------------------------------------------------------------------
------------------------------------------------------------------------------
-- Natools.References implements reference-counted smart pointer to any --
-- type of objects. --
-- This is a basic implementation that does not support weak references or --
-- concurrency. However since there is no internal state, operations on --
-- non-overlapping objects should be thread-safe. --
------------------------------------------------------------------------------
with Ada.Finalization;
generic
type Held_Data (<>) is limited private;
package Natools.References is
pragma Preelaborate (References);
type Reference is new Ada.Finalization.Controlled with private;
type Accessor (Data : not null access constant Held_Data) is
limited private;
type Mutator (Data : not null access Held_Data) is
limited private;
function Create
(Constructor : not null access function return Held_Data)
return Reference;
-- Create a new held object and return a reference to it
procedure Replace
(Ref : in out Reference;
Constructor : not null access function return Held_Data);
-- Replace the object held in Ref with a newly created object
procedure Reset (Ref : in out Reference);
-- Empty Ref
function Is_Empty (Ref : Reference) return Boolean;
-- Check whether Ref refers to an actual object
function "=" (Left, Right : Reference) return Boolean;
-- Check whether Left and Right refer to the same object
function Query (Ref : in Reference) return Accessor;
pragma Inline (Query);
-- Return a derefenciable constant access to the held object
function Update (Ref : in Reference) return Mutator;
pragma Inline (Update);
-- Return a derefenciable mutable access to the held object
procedure Query
(Ref : in Reference;
Process : not null access procedure (Object : in Held_Data));
-- Call Process with the held object
procedure Update
(Ref : in Reference;
Process : not null access procedure (Object : in out Held_Data));
-- Call Process with the held object
Null_Reference : constant Reference;
private
type Counter is new Natural;
type Counter_Access is access Counter;
type Data_Access is access Held_Data;
type Reference is new Ada.Finalization.Controlled with record
Count : Counter_Access := null;
Data : Data_Access := null;
end record;
overriding procedure Adjust (Object : in out Reference);
-- Increate reference counter
overriding procedure Finalize (Object : in out Reference);
-- Decrease reference counter and release memory if needed
type Accessor (Data : not null access constant Held_Data) is limited record
Parent : Reference;
end record;
type Mutator (Data : not null access Held_Data) is limited record
Parent : Reference;
end record;
Null_Reference : constant Reference
:= (Ada.Finalization.Controlled with Count => null, Data => null);
end Natools.References;