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