Geek Gadgets 1

home *** CD-ROM | disk | FTP | other *** search

/ Geek Gadgets 1 / ADE-1.bin / ade-dist / gnat-2.06-src.tgz / tar.out / fsf / gnat / ada / sem_attr.ads < prev next >

Wrap

Text File | 1996-09-28 | 15KB | 333 lines

------------------------------------------------------------------------------ -- -- -- GNAT COMPILER COMPONENTS -- -- -- -- S E M _ A T T R -- -- -- -- S p e c -- -- -- -- $Revision: 1.14 $ -- -- -- -- Copyright (c) 1992,1993,1994,1995 NYU, All Rights Reserved -- -- -- -- 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 2, 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 COPYING. If not, write -- -- to the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. -- -- -- ------------------------------------------------------------------------------ -- Attribute handling is isolated in a separate package to ease the addition -- of implementation defined attributes. Logically this processing belongs -- in chapter 4. See Sem_Ch4 for a description of the relation of the -- Analyze and Resolve routines for expression components. -- This spec also documents all GNAT implementation defined pragmas with Snames; use Snames; with Types; use Types; package Sem_Attr is type Attribute_Class_Array is array (Attribute_Id) of Boolean; -- Type used to build attribute classification flag arrays ----------------------------------------- -- Implementation Dependent Attributes -- ----------------------------------------- -- This section describes the implementation dependent attributes -- provided in GNAT, as well as constructing an array of flags -- indicating which attributes these are. Attribute_Impl_Def : Attribute_Class_Array := Attribute_Class_Array'( ------------------ -- Abort_Signal -- ------------------ Attribute_Abort_Signal => True, -- Standard'Abort_Signal (Standard is the only allowed prefix) -- provides the entity for the special exception used to signal -- task abort or asynchronous transfer of control. Normally this -- attribute should only be used in the tasking runtime (it is -- highly peculiar, and completely outside the normal semantics -- of Ada, for a user program to intercept the abort exception). ------------------ -- Address_Size -- ------------------ Attribute_Address_Size => True, -- Standard'Address_Size (Standard is the only allowed prefix) is -- a static constant giving the number of bits in an Address. It -- is used primarily for constructing the definition of Memory_Size -- in package Standard, but may be freely used in user programs. ----------------------- -- Default_Bit_Order -- ----------------------- Attribute_Default_Bit_Order => True, -- Standard'Default_Bit_Order (Standard is the only permissible prefix), -- provides the value System.Default_Bit_Order as a Pos value (0 for -- High_Order_First, 1 for Low_Order_First). This is used to construct -- the definition of Default_Bit_Order in package System. --------------- -- Elab_Body -- --------------- Attribute_Elab_Body => True, -- This attribute can only be applied to a program unit name. It -- returns the entity for the corresponding elaboration procedure -- for elaborating the body of the referenced unit. This is used -- in the main generated elaboration procedure by the binder, and -- is not normally used in any other context, but there may be -- specialized situations in which it is useful to be able to -- call this elaboration procedure from Ada code, e.g. if it -- is necessary to do selective reelaboration to fix some error. --------------- -- Elab_Spec -- --------------- Attribute_Elab_Spec => True, -- This attribute can only be applied to a program unit name. It -- returns the entity for the corresponding elaboration procedure -- for elaborating the spec of the referenced unit. This is used -- in the main generated elaboration procedure by the binder, and -- is not normally used in any other context, but there may be -- specialized situations in which it is useful to be able to -- call this elaboration procedure from Ada code, e.g. if it -- is necessary to do selective reelaboration to fix some error. -------------- -- Enum_Rep -- -------------- Attribute_Enum_Rep => True, -- For every enumeration subtype S, S'Enum_Rep denotes a function -- with the following specification: -- -- function S (Arg : S'Base) return universal_integer; -- -- The function returns the representation value for the given -- enumeration value. This will be equal to the 'Pos value in the -- absence of an enumeration representation clause. This is a static -- attribute (i.e. the result is static if the argument is static). ----------------- -- Fixed_Value -- ----------------- Attribute_Fixed_Value => True, -- For every fixed-point type S, S'Fixed_Value denotes a function -- with the following specification: -- -- function Fixed_Value (Arg : universal_integer) return S; -- -- The value returned is the fixed-point value V such that -- -- V = Arg * S'Small -- -- The effect is thus equivalent to first converting the argument -- to the integer type used to represent S, and then doing an -- unchecked conversion to the fixed-point type. This attribute is -- primarily intended for use in implementation of the input-output -- functions for fixed-point values. --------- -- Img -- --------- Attribute_Img => True, -- The 'Img attribute differs from 'Image in that it may be applied -- to objects as well as types, in which case it gives the 'Image -- for the subtype of the object. This is convenient for debugging -- -- Put_Line ("X = " & X'Img); -- -- has the same meaning as the more verbose: -- -- Put_Line ("X = " & Temperature_Type'Image (X)); -- -- where Temperature_Type is the subtype of the object X. ------------------- -- Integer_Value -- ------------------- Attribute_Integer_Value => True, -- For every integer type S, S'Integer_Value denotes a function -- with the following specification: -- -- function Integer_Value (Arg : universal_fixed) return S; -- -- The value returned is the integer value V, such that -- -- Arg = V * fixed-type'Small -- -- The effect is thus equivalent to first doing an unchecked convert -- from the fixed-point type to its corresponding implementation type, -- and then converting the result to the target integer type. This -- attribute is primarily intended for use in implementation of the -- standard input-output functions for fixed-point values. ---------------------------- -- Max_Interrupt_Priority -- ---------------------------- Attribute_Max_Interrupt_Priority => True, -- Standard'Max_Interrupt_Priority (Standard is the only permissible -- prefix), provides the value System.Max_Interrupt_Priority, and is -- intended primarily for constructing this definition in package -- System (see note above in Default_Bit_Order description}. ------------------ -- Max_Priority -- ------------------ Attribute_Max_Priority => True, -- Standard'Max_Priority (Standard is the only permissible prefix) -- provides the value System.Max_Priority, and is intended primarily -- for constructing this definition in package System (see note above -- in Default_Bit_Order description). ----------------------- -- Maximum_Alignment -- ----------------------- Attribute_Maximum_Alignment => True, -- Standard'Maximum_Alignment (Standard is the only permissible prefix) -- provides the maximum useful alignment value for the target. This -- is a static value that can be used to specify the alignment for an -- object, guaranteeing that it is properly aligned in all cases. The -- time this is useful is when an external object is imported and its -- alignment requirements are unknown. ------------------------- -- Passed_By_Reference -- ------------------------- Attribute_Passed_By_Reference => True, -- T'Passed_By_Reference for any subtype T returns a boolean value -- that is true if the type is normally passed by reference and -- false if the type is normally passed by copy in calls. For scalar -- types, the result is always False and is static. For non-scalar -- types, the result is non-static (since it is computed by Gigi). ------------------ -- Range_Length -- ------------------ Attribute_Range_Length => True, -- T'Range_Length for any discrete type T yields the number of -- values represented by the subtype (zero for a null range). The -- result is static for static subtypes. Note that Range_Length -- applied to the index subtype of a one dimensional array always -- gives the same result as Range applied to the array itself. ------------------ -- Storage_Unit -- ------------------ Attribute_Storage_Unit => True, -- Standard'Storage_Unit (Standard is the only permissible prefix) -- provides the value System.Storage_Unit, and is intended primarily -- for constructing this definition in package System (see note above -- in Default_Bit_Order description). ---------- -- Tick -- ---------- Attribute_Tick => True, -- Standard'Tick (Standard is the only permissible prefix) provides -- the value System.Tick, and is intended primarily for constructing -- this definition in package System (see note above in description -- of Default_Bit_Order). ------------------------------ -- Universal_Literal_String -- ------------------------------ Attribute_Universal_Literal_String => True, -- The prefix of 'Universal_Literal_String must be a named number. -- The static result is the string consisting of the characters of -- the number as defined in the original source. This allows the -- user program to access the actual text of named numbers without -- intermediate conversions and without the need to enclose the -- strings in quotes (which would preclude their use as numbers). -- This is used internally for the construction of values of the -- floating-point attributes from the file ttypef.ads, but may -- also be used by user programs. ------------------------- -- Unrestricted_Access -- ------------------------- Attribute_Unrestricted_Access => True, -- The Unrestricted_Access attribute is similar to Access except that -- all accessibility and aliased view checks are omitted. This is very -- much a user-beware attribute. Basically its status is very similar -- to Address, for which it is a desirable replacement where the value -- desired is an access type. In other words, its effect is identical -- to first taking 'Address and then doing an unchecked conversion to -- a desired access type. Note that in GNAT, but not necessarily in -- other implementations, the use of static chains for inner level -- subprograms means that Unrestricted_Access applied to a subprogram -- yields a value that can be called as long as the subprogram is in -- scope (normal Ada 95 accessibility rules restrict this usage). --------------- -- Word_Size -- --------------- Attribute_Word_Size => True, -- Standard'Word_Size (Standard is the only permissible prefix) -- provides the value System.Word_Size, and is intended primarily -- for constructing this definition in package System (see note above -- in Default_Bit_Order description). others => False); ----------------- -- Subprograms -- ----------------- procedure Analyze_Attribute (N : Node_Id); -- Performs bottom up semantic analysis of an attribute. Note that the -- parser has already checked that type returning attributes appear only -- in appropriate contexts (i.e. in subtype marks, or as prefixes for -- other attributes). procedure Eval_Attribute (N : Node_Id); -- Performs compile time evaluation of attributes where possible, leaving -- the Is_Static_Expression/Raises_Constraint_Error flags appropriately -- set, and replacing the node with a literal node if the value can be -- computed at compile time. All static attribute references are folded, -- as well as a number of cases of non-static attributes that can always -- be computed at compile time (e.g. floating-point model attributes that -- are applied to non-static subtypes). Of course in such cases, the -- Is_Static_Expression flag will not be set on the resulting literal. procedure Resolve_Attribute (N : Node_Id; Typ : Entity_Id); -- Performs type resolution of attribute. If the attribute yields -- a universal value, mark its type as that of the context. On -- the other hand, if the context itself is universal (as in -- T'Val (T'Pos (X)), mark the type as being the largest type of -- that class that can be used at run-time. This is correct since -- either the value gets folded (in which case it doesn't matter -- what type of the class we give if, since the folding uses universal -- arithmetic anyway) or it doesn't get folded (in which case it is -- going to be dealt with at runtime, and the largest type is right). end Sem_Attr;