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------------------------------------------------------------------------------
-- --
-- GNAT LIBRARY COMPONENTS --
-- --
-- A D A . C O N T A I N E R S . B O U N D E D _ H O L D E R S --
-- --
-- S p e c --
-- --
-- Copyright (C) 2015, Free Software Foundation, Inc. --
-- --
-- This specification is derived from the Ada Reference Manual for use with --
-- GNAT. The copyright notice above, and the license provisions that follow --
-- apply solely to the contents of the part following the private keyword. --
-- --
-- GNAT is free software; you can redistribute it and/or modify it under --
-- terms of the GNU General Public License as published by the Free Soft- --
-- ware Foundation; either version 3, or (at your option) any later ver- --
-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
-- 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/>. --
------------------------------------------------------------------------------
private with System;
generic
type Element_Type (<>) is private;
Max_Size_In_Storage_Elements : Natural :=
Element_Type'Max_Size_In_Storage_Elements;
with function "=" (Left, Right : Element_Type) return Boolean is <>;
package Ada.Containers.Bounded_Holders is
pragma Annotate (CodePeer, Skip_Analysis);
-- This package is patterned after Ada.Containers.Indefinite_Holders. It is
-- used to treat indefinite subtypes as definite, but without using heap
-- allocation. For example, you might like to say:
--
-- type A is array (...) of T'Class; -- illegal
--
-- Instead, you can instantiate this package with Element_Type => T'Class,
-- and say:
--
-- type A is array (...) of Holder;
--
-- Each object of type Holder is allocated Max_Size_In_Storage_Elements
-- bytes. If you try to create a holder from an object of type Element_Type
-- that is too big, an exception is raised (assuming assertions are
-- enabled). This applies to To_Holder and Set. If you pass an Element_Type
-- object that is smaller than Max_Size_In_Storage_Elements, it works fine,
-- but some space is wasted.
--
-- NOTE: If assertions are disabled, and you try to use an Element that is
-- too big, execution is erroneous, and anything can happen, such as
-- overwriting arbitrary memory locations.
--
-- Element_Type must not be an unconstrained array type. It can be a
-- class-wide type or a type with non-defaulted discriminants.
--
-- The 'Size of each Element_Type object must be a multiple of
-- System.Storage_Unit; e.g. creating Holders from 5-bit objects won't
-- work.
type Holder is private;
function "=" (Left, Right : Holder) return Boolean;
function To_Holder (New_Item : Element_Type) return Holder;
function "+" (New_Item : Element_Type) return Holder renames To_Holder;
function Get (Container : Holder) return Element_Type;
procedure Set (Container : in out Holder; New_Item : Element_Type);
private
-- The implementation uses low-level tricks (Address clauses and unchecked
-- conversions of access types) to treat the elements as storage arrays.
pragma Assert (Element_Type'Alignment <= Standard'Maximum_Alignment);
-- This prevents elements with a user-specified Alignment that is too big
type Storage_Element is mod System.Storage_Unit;
type Storage_Array is array (Positive range <>) of Storage_Element;
type Holder is record
Data : Storage_Array (1 .. Max_Size_In_Storage_Elements);
end record
with Alignment => Standard'Maximum_Alignment;
-- We would like to say "Alignment => Element_Type'Alignment", but that
-- is illegal because it's not static, so we use the maximum possible
-- (default) alignment instead.
type Element_Access is access all Element_Type;
pragma Assert (Element_Access'Size = Standard'Address_Size,
"cannot instantiate with an array type");
-- If Element_Access is a fat pointer, Element_Type must be an
-- unconstrained array, which is not allowed. Arrays won't work, because
-- the 'Address of an array points to the first element, thus losing the
-- bounds.
pragma No_Strict_Aliasing (Element_Access);
-- Needed because we are unchecked-converting from Address to
-- Element_Access (see package body), which is a violation of the
-- normal aliasing rules enforced by gcc.
end Ada.Containers.Bounded_Holders;
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