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------------------------------------------------------------------------------ -- -- -- GNAT COMPILER COMPONENTS -- -- -- -- I T Y P E S -- -- -- -- S p e c -- -- -- -- Copyright (C) 1992-2008, Free Software Foundation, Inc. -- -- -- -- GNAT is free software; you can redistribute it and/or modify it under -- -- terms of the GNU General Public License as published by the Free Soft- -- -- ware Foundation; either version 3, or (at your option) any later ver- -- -- sion. GNAT is distributed in the hope that it will be useful, but WITH- -- -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY -- -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License -- -- for more details. You should have received a copy of the GNU General -- -- Public License distributed with GNAT; see file COPYING3. If not, go to -- -- http://www.gnu.org/licenses for a complete copy of the license. -- -- -- -- GNAT was originally developed by the GNAT team at New York University. -- -- Extensive contributions were provided by Ada Core Technologies Inc. -- -- -- ------------------------------------------------------------------------------ -- This package contains declarations for handling of implicit types with Einfo; use Einfo; with Sem_Util; use Sem_Util; with Types; use Types; package Itypes is -------------------- -- Implicit Types -- -------------------- -- Implicit types (Itypes) are types and subtypes created by the semantic -- phase or the expander to reflect the underlying semantics. These could -- be generated by building trees for corresponding declarations and then -- analyzing these trees, but there are three reasons for not doing this -- in some cases: -- 1. The declarations would require more tree nodes -- 2. In some cases, the elaboration of these types is associated -- with internal nodes in the tree. -- 3. For some types, notably class wide types, there is no Ada -- declaration that would correspond to the desired entity. -- So instead, implicit types are constructed by simply creating an -- appropriate entity with the help of routines in this package. These -- entities are fully decorated, as described in Einfo (just as though -- they had been created by the normal analysis procedure). -- The type declaration declaring an Itype must be analyzed with checks -- off because this declaration has not been inserted in the tree (if it -- has been then it is not an Itype), and hence checks that would be -- generated during the analysis cannot be inserted in the tree. At any -- rate, Itype analysis should always be done with checks off, otherwise -- duplicate checks will most likely be emitted. -- Unlike types declared explicitly, implicit types are defined on first -- use, which means that Gigi detects the use of such types, and defines -- them at the point of the first use automatically. -- Although Itypes are not explicitly declared, they are associated with -- a specific node in the tree (roughly the node that caused them to be -- created), via the Associated_Node_For_Itype field. This association is -- used particularly by New_Copy_Tree, which uses it to determine whether -- or not to copy a referenced Itype. If the associated node is part of -- the tree to be copied by New_Copy_Tree, then (since the idea of the -- call to New_Copy_Tree is to create a complete duplicate of a tree, -- as though it had appeared separately in the source), the Itype in -- question is duplicated as part of the New_Copy_Tree processing. -- As a consequence of this copying mechanism, the association between -- Itypes and associated nodes must be one-to-one: several Itypes must -- not share an associated node. For example, the semantic decoration -- of an array aggregate generates several Itypes: for each index subtype -- and for the array subtype. The associated node of each index subtype -- is the corresponding range expression. -- Notes on the use of the Parent field of an Itype -- In some cases, we do create a declaration node for an itype, and in -- such cases, the Parent field of the Itype points to this declaration -- in the normal manner. This case can be detected by checking for a -- non-empty Parent field referencing a declaration whose Defining_Entity -- is the Itype in question. -- In some other cases, where we don't generate such a declaration, as -- described above, the Itype is attached to the tree implicitly by being -- referenced elsewhere, e.g. as the Etype of some object. In this case -- the Parent field may be Empty. -- In other cases where we don't generate a declaration for the Itype, -- the Itype may be attached to an arbitrary node in the tree, using -- the Parent field. This Parent field may even reference a declaration -- for a related different entity (hence the description of the tests -- needed for the case where a declaration for the Itype is created). ------------------ -- Create_Itype -- ------------------ function Create_Itype (Ekind : Entity_Kind; Related_Nod : Node_Id; Related_Id : Entity_Id := Empty; Suffix : Character := ' '; Suffix_Index : Nat := 0; Scope_Id : Entity_Id := Current_Scope) return Entity_Id; -- Used to create a new Itype -- -- Related_Nod is the node for which this Itype was created. It is -- set as the Associated_Node_For_Itype of the new Itype. The Sloc of -- the new Itype is that of this node. -- -- Related_Id is present only if the implicit type name may be referenced -- as a public symbol, and thus needs a unique external name. The name -- is created by a call to: -- -- New_External_Name (Chars (Related_Id), Suffix, Suffix_Index, 'T') -- -- If the implicit type does not need an external name, then the -- Related_Id parameter is omitted (and hence Empty). In this case -- Suffix and Suffix_Index are ignored and the implicit type name is -- created by a call to New_Internal_Name ('T'). -- -- Note that in all cases, the name starts with "T". This is used -- to identify implicit types in the error message handling circuits. -- -- The Scope_Id parameter specifies the scope of the created type, and -- is normally the Current_Scope as shown, but can be set otherwise. -- -- The size/align fields are initialized to unknown (Uint_0). -- -- If Ekind is in Access_Subprogram_Kind, Can_Use_Internal_Rep is set True, -- unless Always_Compatible_Rep_On_Target is True. --------------------------------- -- Create_Null_Excluding_Itype -- --------------------------------- function Create_Null_Excluding_Itype (T : Entity_Id; Related_Nod : Node_Id; Scope_Id : Entity_Id := Current_Scope) return Entity_Id; -- Ada 2005 (AI-231): T is an access type and this subprogram creates and -- returns an internal access-subtype declaration of T that has the null -- exclusion attribute set to True. -- -- Usage of null-excluding Itypes -- ------------------------------ -- -- type T1 is access ... -- type T2 is not null T1; -- -- type Rec is record -- Comp : not null T1; -- end record; -- -- type Arr is array (...) of not null T1; -- -- Instead of associating the not-null attribute with the defining ids of -- these declarations, we generate an internal subtype declaration of T1 -- that has the null exclusion attribute set to true. end Itypes;
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