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 3, 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 COPYING3. If not, go to --
19 -- http://www.gnu.org/licenses for a complete copy of the license. --
21 -- GNAT was originally developed by the GNAT team at New York University. --
22 -- Extensive contributions were provided by Ada Core Technologies Inc. --
24 ------------------------------------------------------------------------------
26 -- This package contains declarations for handling of implicit types
28 with Einfo
; use Einfo
;
29 with Sem_Util
; use Sem_Util
;
30 with Types
; use Types
;
38 -- Implicit types (Itypes) are types and subtypes created by the semantic
39 -- phase or the expander to reflect the underlying semantics. These could
40 -- be generated by building trees for corresponding declarations and then
41 -- analyzing these trees, but there are three reasons for not doing this:
43 -- 1. The declarations would require more tree nodes
45 -- 2. In some cases, the elaboration of these types is associated
46 -- with internal nodes in the tree.
48 -- 3. For some types, notably class wide types, there is no Ada
49 -- declaration that would correspond to the desired entity.
51 -- So instead, implicit types are constructed by simply creating an
52 -- appropriate entity with the help of routines in this package. These
53 -- entities are fully decorated, as described in Einfo (just as though
54 -- they had been created by the normal analysis procedure).
56 -- The type declaration declaring an Itype must be analyzed with checks
57 -- off because this declaration has not been inserted in the tree (if it
58 -- has been then it is not an Itype), and hence checks that would be
59 -- generated during the analysis cannot be inserted in the tree. At any
60 -- rate, Itype analysis should always be done with checks off, otherwise
61 -- duplicate checks will most likely be emitted.
63 -- Unlike types declared explicitly, implicit types are defined on first
64 -- use, which means that Gigi detects the use of such types, and defines
65 -- them at the point of the first use automatically.
67 -- Although Itypes are not explicitly declared, they are associated with
68 -- a specific node in the tree (roughly the node that caused them to be
69 -- created), via the Associated_Node_For_Itype field. This association is
70 -- used particularly by New_Copy_Tree, which uses it to determine whether
71 -- or not to copy a referenced Itype. If the associated node is part of
72 -- the tree to be copied by New_Copy_Tree, then (since the idea of the
73 -- call to New_Copy_Tree is to create a complete duplicate of a tree,
74 -- as though it had appeared separately in the source), the Itype in
75 -- 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 -- If Ekind is in Access_Subprogram_Type_Kind, Can_Use_Internal_Rep is set
119 -- True, unless Always_Compatible_Rep_On_Target is True.
121 ---------------------------------
122 -- Create_Null_Excluding_Itype --
123 ---------------------------------
125 function Create_Null_Excluding_Itype
127 Related_Nod
: Node_Id
;
128 Scope_Id
: Entity_Id
:= Current_Scope
) return Entity_Id
;
129 -- Ada 2005 (AI-231): T is an access type and this subprogram creates and
130 -- returns an internal access-subtype declaration of T that has the null
131 -- exclusion attribute set to True.
133 -- Usage of null-excluding Itypes
134 -- ------------------------------
136 -- type T1 is access ...
137 -- type T2 is not null T1;
139 -- type Rec is record
140 -- Comp : not null T1;
143 -- type Arr is array (...) of not null T1;
145 -- Instead of associating the not-null attribute with the defining ids of
146 -- these declarations, we generate an internal subtype declaration of T1
147 -- that has the null exclusion attribute set to true.