type Type_Specific_Data is record
Idepth : Natural;
+ -- Inheritance Depth Level: Used to implement the membership test
+ -- associated with single inheritance of tagged types in constant-time.
+ -- In addition it also indicates the size of the first table stored in
+ -- the Tags_Table component (see comment below).
+
Access_Level : Natural;
+ -- Accessibility level required to give support to Ada 2005 nested type
+ -- extensions. This feature allows safe nested type extensions by
+ -- shifting the accessibility checks to certain operations, rather than
+ -- being enforced at the type declaration. In particular, by performing
+ -- run-time accessibility checks on class-wide allocators, class-wide
+ -- function return, and class-wide stream I/O, the danger of objects
+ -- outliving their type declaration can be eliminated (Ada 2005: AI-344)
+
Expanded_Name : Cstring_Ptr;
External_Tag : Cstring_Ptr;
HT_Link : Tag;
+ -- Components used to give support to the Ada.Tags subprograms described
+ -- in ARM 3.9
+
Remotely_Callable : Boolean;
+ -- Used to check ARM E.4 (18)
+
RC_Offset : SSE.Storage_Offset;
+ -- Controller Offset: Used to give support to tagged controlled objects
+ -- (see Get_Deep_Controller at s-finimp)
+
Num_Interfaces : Natural;
- Tags_Table : Tag_Table (Natural);
+ -- Number of abstract interface types implemented by the tagged type.
+ -- The value Idepth+Num_Interfaces indicates the end of the second table
+ -- stored in the Tags_Table component. It is used to implement the
+ -- membership test associated with interfaces (Ada 2005:AI-251)
+ Tags_Table : Tag_Table (0 .. 1);
-- The size of the Tags_Table array actually depends on the tagged type
-- to which it applies. The compiler ensures that has enough space to
-- store all the entries of the two tables phisically stored there: the
-- "table of ancestor tags" and the "table of interface tags". For this
-- purpose we are using the same mechanism as for the Prims_Ptr array in
- -- the Dispatch_Table record. See comments below for more details.
-
+ -- the Dispatch_Table record. See comments below on Prims_Ptr for
+ -- further details.
end record;
type Dispatch_Table is record
-- Offset_To_Top : Natural;
- -- Typeinfo_Ptr : System.Address; -- Currently TSD is also here???
- Prims_Ptr : Address_Array (Positive);
+ -- Typeinfo_Ptr : System.Address;
+
+ -- According to the C++ ABI the components Offset_To_Top and
+ -- Typeinfo_Ptr are stored just "before" the dispatch table (that is,
+ -- the Prims_Ptr table), and they are referenced with negative offsets
+ -- referring to the base of the dispatch table. The _Tag (or the
+ -- VTable_Ptr in C++ terminology) must point to the base of the virtual
+ -- table, just after these components, to point to the Prims_Ptr table.
+ -- For this purpose the expander generates a Prims_Ptr table that has
+ -- enough space for these additional components, and generates code that
+ -- displaces the _Tag to point after these components.
+
+ Prims_Ptr : Address_Array (1 .. 1);
+ -- The size of the Prims_Ptr array actually depends on the tagged type
+ -- to which it applies. For each tagged type, the expander computes the
+ -- actual array size, allocates the Dispatch_Table record accordingly,
+ -- and generates code that displaces the base of the record after the
+ -- Typeinfo_Ptr component. For this reason the first two components have
+ -- been commented in the previous declaration. The access to these
+ -- components is done by means of local functions.
+ --
+ -- To avoid the use of discriminants to define the actual size of the
+ -- dispatch table, we used to declare the tag as a pointer to a record
+ -- that contains an arbitrary array of addresses, using Positive as its
+ -- index. This ensures that there are never range checks when accessing
+ -- the dispatch table, but it prevents GDB from displaying tagged types
+ -- properly. A better approach is to declare this record type as holding
+ -- small number of addresses, and to explicitly suppress checks on it.
+ --
+ -- Note that in both cases, this type is never allocated, and serves
+ -- only to declare the corresponding access type.
end record;
- -- Note on the commented out fields of the Dispatch_Table
- --
- -- According to the C++ ABI the components Offset_To_Top and Typeinfo_Ptr
- -- are stored just "before" the dispatch table (that is, the Prims_Ptr
- -- table), and they are referenced with negative offsets referring to the
- -- base of the dispatch table. The _Tag (or the VTable_Ptr in C++ termi-
- -- nology) must point to the base of the virtual table, just after these
- -- components, to point to the Prims_Ptr table. For this purpose the
- -- expander generates a Prims_Ptr table that has enough space for these
- -- additional components, and generates code that displaces the _Tag to
- -- point after these components.
-
- -- The size of the Prims_Ptr array actually depends on the tagged type to
- -- which it applies. For each tagged type, the expander computes the
- -- actual array size, allocates the Dispatch_Table record accordingly, and
- -- generates code that displaces the base of the record after the
- -- Typeinfo_Ptr component. For this reason the first two components have
- -- been commented in the previous declaration. The access to these
- -- components is done by means of local functions.
- --
- -- To avoid the use of discriminants to define the actual size of the
- -- dispatch table, we used to declare the tag as a pointer to a record
- -- that contains an arbitrary array of addresses, using Positive as its
- -- index. This ensures that there are never range checks when accessing
- -- the dispatch table, but it prevents GDB from displaying tagged types
- -- properly. A better approach is to declare this record type as holding a
- -- small number of addresses, and to explicitly suppress checks on it.
- --
- -- Note that in both cases, this type is never allocated, and serves only
- -- to declare the corresponding access type.
-
---------------------------------------------
-- Unchecked Conversions for String Fields --
---------------------------------------------
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