1------------------------------------------------------------------------------ 2-- -- 3-- GNAT COMPILER COMPONENTS -- 4-- -- 5-- I T Y P E S -- 6-- -- 7-- S p e c -- 8-- -- 9-- Copyright (C) 1992-2010, 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 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. -- 20-- -- 21-- GNAT was originally developed by the GNAT team at New York University. -- 22-- Extensive contributions were provided by Ada Core Technologies Inc. -- 23-- -- 24------------------------------------------------------------------------------ 25 26-- This package contains declarations for handling of implicit types 27 28with Einfo; use Einfo; 29with Sem_Util; use Sem_Util; 30with Types; use Types; 31 32package Itypes is 33 34 -------------------- 35 -- Implicit Types -- 36 -------------------- 37 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 42 -- in some cases: 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 -- As a consequence of this copying mechanism, the association between 79 -- Itypes and associated nodes must be one-to-one: several Itypes must 80 -- not share an associated node. For example, the semantic decoration 81 -- of an array aggregate generates several Itypes: for each index subtype 82 -- and for the array subtype. The associated node of each index subtype 83 -- is the corresponding range expression. 84 85 -- Notes on the use of the Parent field of an Itype 86 87 -- In some cases, we do create a declaration node for an itype, and in 88 -- such cases, the Parent field of the Itype points to this declaration 89 -- in the normal manner. This case can be detected by checking for a 90 -- non-empty Parent field referencing a declaration whose Defining_Entity 91 -- is the Itype in question. 92 93 -- In some other cases, where we don't generate such a declaration, as 94 -- described above, the Itype is attached to the tree implicitly by being 95 -- referenced elsewhere, e.g. as the Etype of some object. In this case 96 -- the Parent field may be Empty. 97 98 -- In other cases where we don't generate a declaration for the Itype, 99 -- the Itype may be attached to an arbitrary node in the tree, using 100 -- the Parent field. This Parent field may even reference a declaration 101 -- for a related different entity (hence the description of the tests 102 -- needed for the case where a declaration for the Itype is created). 103 104 ------------------ 105 -- Create_Itype -- 106 ------------------ 107 108 function Create_Itype 109 (Ekind : Entity_Kind; 110 Related_Nod : Node_Id; 111 Related_Id : Entity_Id := Empty; 112 Suffix : Character := ' '; 113 Suffix_Index : Nat := 0; 114 Scope_Id : Entity_Id := Current_Scope) return Entity_Id; 115 -- Used to create a new Itype 116 -- 117 -- Related_Nod is the node for which this Itype was created. It is 118 -- set as the Associated_Node_For_Itype of the new Itype. The Sloc of 119 -- the new Itype is that of this node. 120 -- 121 -- Related_Id is present only if the implicit type name may be referenced 122 -- as a public symbol, and thus needs a unique external name. The name 123 -- is created by a call to: 124 -- 125 -- New_External_Name (Chars (Related_Id), Suffix, Suffix_Index, 'T') 126 -- 127 -- If the implicit type does not need an external name, then the 128 -- Related_Id parameter is omitted (and hence Empty). In this case 129 -- Suffix and Suffix_Index are ignored and the implicit type name is 130 -- created by a call to Make_Temporary. 131 -- 132 -- Note that in all cases, the name starts with "T". This is used 133 -- to identify implicit types in the error message handling circuits. 134 -- 135 -- The Scope_Id parameter specifies the scope of the created type, and 136 -- is normally the Current_Scope as shown, but can be set otherwise. 137 -- 138 -- The size/align fields are initialized to unknown (Uint_0). 139 -- 140 -- If Ekind is in Access_Subprogram_Kind, Can_Use_Internal_Rep is set True, 141 -- unless Always_Compatible_Rep_On_Target is True. 142 143 --------------------------------- 144 -- Create_Null_Excluding_Itype -- 145 --------------------------------- 146 147 function Create_Null_Excluding_Itype 148 (T : Entity_Id; 149 Related_Nod : Node_Id; 150 Scope_Id : Entity_Id := Current_Scope) return Entity_Id; 151 -- Ada 2005 (AI-231): T is an access type and this subprogram creates and 152 -- returns an internal access-subtype declaration of T that has the null 153 -- exclusion attribute set to True. 154 -- 155 -- Usage of null-excluding Itypes 156 -- ------------------------------ 157 -- 158 -- type T1 is access ... 159 -- type T2 is not null T1; 160 -- 161 -- type Rec is record 162 -- Comp : not null T1; 163 -- end record; 164 -- 165 -- type Arr is array (...) of not null T1; 166 -- 167 -- Instead of associating the not-null attribute with the defining ids of 168 -- these declarations, we generate an internal subtype declaration of T1 169 -- that has the null exclusion attribute set to true. 170 171end Itypes; 172