1 ------------------------------------------------------------------------------
3 -- GNAT COMPILER COMPONENTS --
9 -- Copyright (C) 1992-2007, Free Software Foundation, Inc. --
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. --
22 -- GNAT was originally developed by the GNAT team at New York University. --
23 -- Extensive contributions were provided by Ada Core Technologies Inc. --
25 ------------------------------------------------------------------------------
27 -- This package contains declarations for handling of implicit types
29 with Einfo; use Einfo;
30 with Sem_Util; use Sem_Util;
31 with Types; use Types;
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:
44 -- 1. The declarations would require more tree nodes
46 -- 2. In some cases, the elaboration of these types is associated
47 -- with internal nodes in the tree.
49 -- 3. For some types, notably class wide types, there is no Ada
50 -- declaration that would correspond to the desired entity.
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).
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.
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.
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 -- As a consequence of this copying mechanism, the association between
78 -- itypes and associated nodes must be one-to-one: several itypes must
79 -- not share an associated node. For example, the semantic decoration
80 -- of an array aggregate generates several itypes: for each index subtype
81 -- and for the array subtype. The associated node of each index subtype
82 -- is the corresponding range expression.
90 Related_Nod : Node_Id;
91 Related_Id : Entity_Id := Empty;
92 Suffix : Character := ' ';
93 Suffix_Index : Nat := 0;
94 Scope_Id : Entity_Id := Current_Scope) return Entity_Id;
95 -- Used to create a new Itype.
97 -- Related_Nod is the node for which this Itype was created. It is
98 -- set as the Associated_Node_For_Itype of the new itype. The Sloc of
99 -- the new Itype is that of this node.
101 -- Related_Id is present only if the implicit type name may be referenced
102 -- as a public symbol, and thus needs a unique external name. The name
103 -- is created by a call to:
105 -- New_External_Name (Chars (Related_Id), Suffix, Suffix_Index, 'T')
107 -- If the implicit type does not need an external name, then the
108 -- Related_Id parameter is omitted (and hence Empty). In this case
109 -- Suffix and Suffix_Index are ignored and the implicit type name is
110 -- created by a call to New_Internal_Name ('T').
112 -- Note that in all cases, the name starts with "T". This is used
113 -- to identify implicit types in the error message handling circuits.
115 -- The Scope_Id parameter specifies the scope of the created type, and
116 -- is normally the Current_Scope as shown, but can be set otherwise.
118 ---------------------------------
119 -- Create_Null_Excluding_Itype --
120 ---------------------------------
122 function Create_Null_Excluding_Itype
124 Related_Nod : Node_Id;
125 Scope_Id : Entity_Id := Current_Scope) return Entity_Id;
126 -- Ada 2005 (AI-231): T is an access type and this subprogram creates and
127 -- returns an internal access-subtype declaration of T that has the null
128 -- exclusion attribute set to True.
130 -- Usage of null-excluding itypes
131 -- ------------------------------
133 -- type T1 is access ...
134 -- type T2 is not null T1;
136 -- type Rec is record
137 -- Comp : not null T1;
140 -- type Arr is array (...) of not null T1;
142 -- Instead of associating the not-null attribute with the defining ids of
143 -- these declarations, we generate an internal subtype declaration of T1
144 -- that has the null exclusion attribute set to true.