gcc/ada/itypes.ads

   1 ------------------------------------------------------------------------------
   2 --                                                                          --
   3 --                         GNAT COMPILER COMPONENTS                         --
   4 --                                                                          --
   5 --                               I T Y P E S                                --
   6 --                                                                          --
   7 --                                 S p e c                                  --
   8 --                                                                          --
   9 --          Copyright (C) 1992-2005, Free Software Foundation, Inc.         --
  10 --                                                                          --
  11 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
  12 -- terms of the  GNU General Public License as published  by the Free Soft- --
  13 -- ware  Foundation;  either version 2,  or (at your option) any later ver- --
  14 -- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
  15 -- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
  16 -- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --
  17 -- for  more details.  You should have  received  a copy of the GNU General --
  18 -- Public License  distributed with GNAT;  see file COPYING.  If not, write --
  19 -- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --
  20 -- Boston, MA 02110-1301, USA.                                              --
  21 --                                                                          --
  22 -- GNAT was originally developed  by the GNAT team at  New York University. --
  23 -- Extensive contributions were provided by Ada Core Technologies Inc.      --
  24 --                                                                          --
  25 ------------------------------------------------------------------------------
  26
  27 --  This package contains declarations for handling of implicit types
  28
  29 with Einfo;    use Einfo;
  30 with Sem_Util; use Sem_Util;
  31 with Types;    use Types;
  32
  33 package Itypes is
  34
  35    --------------------
  36    -- Implicit Types --
  37    --------------------
  38
  39    --  Implicit types are types and subtypes created by the semantic phase
  40    --  or the expander to reflect the underlying semantics. These could be
  41    --  generated by building trees for corresponding declarations and then
  42    --  analyzing these trees, but there are three reasons for not doing this:
  43
  44    --    1. The declarations would require more tree nodes
  45
  46    --    2. In some cases, the elaboration of these types is associated
  47    --       with internal nodes in the tree.
  48
  49    --    3. For some types, notably class wide types, there is no Ada
  50    --       declaration that would correspond to the desired entity.
  51
  52    --  So instead, implicit types are constructed by simply creating an
  53    --  appropriate entity with the help of routines in this package. These
  54    --  entities are fully decorated, as described in Einfo (just as though
  55    --  they had been created by the normal analysis procedure).
  56
  57    --  The type declaration declaring an Itype must be analyzed with checks
  58    --  off because this declaration has not been inserted in the tree (if it
  59    --  has been then it is not an itype), and hence checks that would be
  60    --  generated during the analysis cannot be inserted in the tree. At any
  61    --  rate, itype analysis should always be done with checks off, otherwise
  62    --  duplicate checks will most likely be emitted.
  63
  64    --  Unlike types declared explicitly, implicit types are defined on first
  65    --  use, which means that Gigi detects the use of such types, and defines
  66    --  them at the point of the first use automatically.
  67
  68    --  Although Itypes are not explicitly declared, they are associated with
  69    --  a specific node in the tree (roughly the node that caused them to be
  70    --  created), via the Associated_Node_For_Itype field. This association is
  71    --  used particularly by New_Copy_Tree, which uses it to determine whether
  72    --  or not to copy a referenced Itype. If the associated node is part of
  73    --  the tree to be copied by New_Copy_Tree, then (since the idea of the
  74    --  call to New_Copy_Tree is to create a complete duplicate of a tree,
  75    --  as though it had appeared separately in the source), the Itype in
  76    --  question is duplicated as part of the New_Copy_Tree processing.
  77
  78    -----------------
  79    -- Subprograms --
  80    -----------------
  81
  82    function Create_Itype
  83      (Ekind        : Entity_Kind;
  84       Related_Nod  : Node_Id;
  85       Related_Id   : Entity_Id := Empty;
  86       Suffix       : Character := ' ';
  87       Suffix_Index : Nat       := 0;
  88       Scope_Id     : Entity_Id := Current_Scope) return Entity_Id;
  89    --  Used to create a new Itype.
  90    --
  91    --   Related_Nod is the node for which this Itype was created.  It is
  92    --   set as the Associated_Node_For_Itype of the new itype.  The Sloc of
  93    --   the new Itype is that of this node.
  94    --
  95    --   Related_Id is present only if the implicit type name may be referenced
  96    --   as a public symbol, and thus needs a unique external name. The name
  97    --   is created by a call to:
  98    --
  99    --     New_External_Name (Chars (Related_Id), Suffix, Suffix_Index, 'T')
 100    --
 101    --   If the implicit type does not need an external name, then the
 102    --   Related_Id parameter is omitted (and hence Empty). In this case
 103    --   Suffix and Suffix_Index are ignored and the implicit type name is
 104    --   created by a call to New_Internal_Name ('T').
 105    --
 106    --   Note that in all cases, the name starts with "T". This is used
 107    --   to identify implicit types in the error message handling circuits.
 108    --
 109    --  The Scope_Id parameter specifies the scope of the created type, and
 110    --  is normally the Current_Scope as shown, but can be set otherwise.
 111
 112    ---------------------------------
 113    -- Create_Null_Excluding_Itype --
 114    ---------------------------------
 115
 116    function Create_Null_Excluding_Itype
 117       (T           : Entity_Id;
 118        Related_Nod : Node_Id;
 119        Scope_Id    : Entity_Id := Current_Scope) return Entity_Id;
 120    --  Ada 2005 (AI-231): T is an access type and this subprogram creates and
 121    --  returns an internal access-subtype declaration of T that has the null
 122    --  exclusion attribute set to True.
 123    --
 124    --  Usage of null-excluding itypes
 125    --  ------------------------------
 126    --
 127    --      type T1 is access ...
 128    --      type T2 is not null T1;
 129    --
 130    --      type Rec is record
 131    --         Comp : not null T1;
 132    --      end record;
 133    --
 134    --      type Arr is array (...) of not null T1;
 135    --
 136    --  Instead of associating the not-null attribute with the defining ids of
 137    --  these declarations, we generate an internal subtype declaration of T1
 138    --  that has the null exclusion attribute set to true.
 139
 140 end Itypes;