gnat_rm.texi

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@smallexample @c ada
pragma Complex_Representation
        ([Entity =>] LOCAL_NAME);
@end smallexample

@noindent
The @var{Entity} argument must be the name of a record type which has
two fields of the same floating-point type.  The effect of this pragma is
to force gcc to use the special internal complex representation form for
this record, which may be more efficient.  Note that this may result in
the code for this type not conforming to standard ABI (application
binary interface) requirements for the handling of record types.  For
example, in some environments, there is a requirement for passing
records by pointer, and the use of this pragma may result in passing
this type in floating-point registers.

@node Pragma Component_Alignment
@unnumberedsec Pragma Component_Alignment
@cindex Alignments of components
@findex Component_Alignment
@noindent
Syntax:

@smallexample @c ada
pragma Component_Alignment (
     [Form =>] ALIGNMENT_CHOICE
  [, [Name =>] type_LOCAL_NAME]);

ALIGNMENT_CHOICE ::=
  Component_Size
| Component_Size_4
| Storage_Unit
| Default
@end smallexample

@noindent
Specifies the alignment of components in array or record types.
The meaning of the @var{Form} argument is as follows:

@table @code
@findex Component_Size
@item Component_Size
Aligns scalar components and subcomponents of the array or record type
on boundaries appropriate to their inherent size (naturally
aligned).  For example, 1-byte components are aligned on byte boundaries,
2-byte integer components are aligned on 2-byte boundaries, 4-byte
integer components are aligned on 4-byte boundaries and so on.  These
alignment rules correspond to the normal rules for C compilers on all
machines except the VAX@.

@findex Component_Size_4
@item Component_Size_4
Naturally aligns components with a size of four or fewer
bytes.  Components that are larger than 4 bytes are placed on the next
4-byte boundary.

@findex Storage_Unit
@item Storage_Unit
Specifies that array or record components are byte aligned, i.e.@:
aligned on boundaries determined by the value of the constant
@code{System.Storage_Unit}.

@cindex OpenVMS
@item Default
Specifies that array or record components are aligned on default
boundaries, appropriate to the underlying hardware or operating system or
both.  For OpenVMS VAX systems, the @code{Default} choice is the same as
the @code{Storage_Unit} choice (byte alignment).  For all other systems,
the @code{Default} choice is the same as @code{Component_Size} (natural
alignment).
@end table

@noindent
If the @code{Name} parameter is present, @var{type_LOCAL_NAME} must
refer to a local record or array type, and the specified alignment
choice applies to the specified type.  The use of
@code{Component_Alignment} together with a pragma @code{Pack} causes the
@code{Component_Alignment} pragma to be ignored.  The use of
@code{Component_Alignment} together with a record representation clause
is only effective for fields not specified by the representation clause.

If the @code{Name} parameter is absent, the pragma can be used as either
a configuration pragma, in which case it applies to one or more units in
accordance with the normal rules for configuration pragmas, or it can be
used within a declarative part, in which case it applies to types that
are declared within this declarative part, or within any nested scope
within this declarative part.  In either case it specifies the alignment
to be applied to any record or array type which has otherwise standard
representation.

If the alignment for a record or array type is not specified (using
pragma @code{Pack}, pragma @code{Component_Alignment}, or a record rep
clause), the GNAT uses the default alignment as described previously.

@node Pragma Convention_Identifier
@unnumberedsec Pragma Convention_Identifier
@findex Convention_Identifier
@cindex Conventions, synonyms
@noindent
Syntax:

@smallexample @c ada
pragma Convention_Identifier (
         [Name =>]       IDENTIFIER,
         [Convention =>] convention_IDENTIFIER);
@end smallexample

@noindent
This pragma provides a mechanism for supplying synonyms for existing
convention identifiers. The @code{Name} identifier can subsequently
be used as a synonym for the given convention in other pragmas (including
for example pragma @code{Import} or another @code{Convention_Identifier}
pragma). As an example of the use of this, suppose you had legacy code
which used Fortran77 as the identifier for Fortran. Then the pragma:

@smallexample @c ada
pragma Convention_Identifier (Fortran77, Fortran);
@end smallexample

@noindent
would allow the use of the convention identifier @code{Fortran77} in
subsequent code, avoiding the need to modify the sources. As another
example, you could use this to parametrize convention requirements
according to systems. Suppose you needed to use @code{Stdcall} on
windows systems, and @code{C} on some other system, then you could
define a convention identifier @code{Library} and use a single
@code{Convention_Identifier} pragma to specify which convention
would be used system-wide.

@node Pragma CPP_Class
@unnumberedsec Pragma CPP_Class
@findex CPP_Class
@cindex Interfacing with C++
@noindent
Syntax:

@smallexample @c ada
pragma CPP_Class ([Entity =>] LOCAL_NAME);
@end smallexample

@noindent
The argument denotes an entity in the current declarative region that is
declared as a tagged record type. It indicates that the type corresponds
to an externally declared C++ class type, and is to be laid out the same
way that C++ would lay out the type.

Types for which @code{CPP_Class} is specified do not have assignment or
equality operators defined (such operations can be imported or declared
as subprograms as required). Initialization is allowed only by constructor
functions (see pragma @code{CPP_Constructor}). Such types are implicitly
limited if not explicitly declared as limited or derived from a limited
type, and a warning is issued in that case.

Pragma @code{CPP_Class} is intended primarily for automatic generation
using an automatic binding generator tool.
See @ref{Interfacing to C++} for related information.

Note: Pragma @code{CPP_Class} is currently obsolete. It is supported
for backward compatibility but its functionality is available
using pragma @code{Import} with @code{Convention} = @code{CPP}.

@node Pragma CPP_Constructor
@unnumberedsec Pragma CPP_Constructor
@cindex Interfacing with C++
@findex CPP_Constructor
@noindent
Syntax:

@smallexample @c ada
pragma CPP_Constructor ([Entity =>] LOCAL_NAME
  [, [External_Name =>] static_string_EXPRESSION ]
  [, [Link_Name     =>] static_string_EXPRESSION ]);
@end smallexample

@noindent
This pragma identifies an imported function (imported in the usual way
with pragma @code{Import}) as corresponding to a C++ constructor. If
@code{External_Name} and @code{Link_Name} are not specified then the
@code{Entity} argument is a name that must have been previously mentioned
in a pragma @code{Import} with @code{Convention} = @code{CPP}. Such name
must be of one of the following forms:

@itemize @bullet
@item
@code{function @var{Fname} return @var{T}'Class}

@item
@code{function @var{Fname} (@dots{}) return @var{T}'Class}
@end itemize

@noindent
where @var{T} is a tagged type to which the pragma @code{CPP_Class} applies.

The first form is the default constructor, used when an object of type
@var{T} is created on the Ada side with no explicit constructor.  Other
constructors (including the copy constructor, which is simply a special
case of the second form in which the one and only argument is of type
@var{T}), can only appear in two contexts:

@itemize @bullet
@item
On the right side of an initialization of an object of type @var{T}.
@item
In an extension aggregate for an object of a type derived from @var{T}.
@end itemize

@noindent
Although the constructor is described as a function that returns a value
on the Ada side, it is typically a procedure with an extra implicit
argument (the object being initialized) at the implementation
level.  GNAT issues the appropriate call, whatever it is, to get the
object properly initialized.

In the case of derived objects, you may use one of two possible forms
for declaring and creating an object:

@itemize @bullet
@item @code{New_Object : Derived_T}
@item @code{New_Object : Derived_T := (@var{constructor-call with} @dots{})}
@end itemize

@noindent
In the first case the default constructor is called and extension fields
if any are initialized according to the default initialization
expressions in the Ada declaration.  In the second case, the given
constructor is called and the extension aggregate indicates the explicit
values of the extension fields.

If no constructors are imported, it is impossible to create any objects
on the Ada side.  If no default constructor is imported, only the
initialization forms using an explicit call to a constructor are
permitted.

Pragma @code{CPP_Constructor} is intended primarily for automatic generation
using an automatic binding generator tool.
See @ref{Interfacing to C++} for more related information.

@node Pragma CPP_Virtual
@unnumberedsec Pragma CPP_Virtual
@cindex Interfacing to C++
@findex CPP_Virtual
@noindent
This pragma is now obsolete has has no effect because GNAT generates
the same object layout than the G++ compiler.

See @ref{Interfacing to C++} for related information.

@node Pragma CPP_Vtable
@unnumberedsec Pragma CPP_Vtable
@cindex Interfacing with C++
@findex CPP_Vtable
@noindent
This pragma is now obsolete has has no effect because GNAT generates
the same object layout than the G++ compiler.

See @ref{Interfacing to C++} for related information.

@node Pragma Debug
@unnumberedsec Pragma Debug
@findex Debug
@noindent
Syntax:

@smallexample @c ada
pragma Debug ([CONDITION, ]PROCEDURE_CALL_WITHOUT_SEMICOLON);

PROCEDURE_CALL_WITHOUT_SEMICOLON ::=
  PROCEDURE_NAME
| PROCEDURE_PREFIX ACTUAL_PARAMETER_PART
@end smallexample

@noindent
The procedure call argument has the syntactic form of an expression, meeting
the syntactic requirements for pragmas.

If debug pragmas are not enabled or if the condition is present and evaluates
to False, this pragma has no effect. If debug pragmas are enabled, the
semantics of the pragma is exactly equivalent to the procedure call statement
corresponding to the argument with a terminating semicolon. Pragmas are
permitted in sequences of declarations, so you can use pragma @code{Debug} to
intersperse calls to debug procedures in the middle of declarations. Debug
pragmas can be enabled either by use of the command line switch @code{-gnata}
or by use of the configuration pragma @code{Debug_Policy}.

@node Pragma Debug_Policy
@unnumberedsec Pragma Debug_Policy
@findex Debug_Policy
@noindent
Syntax:

@smallexample @c ada
pragma Debug_Policy (CHECK | IGNORE);
@end smallexample

@noindent
If the argument is @code{CHECK}, then pragma @code{DEBUG} is enabled.
If the argument is @code{IGNORE}, then pragma @code{DEBUG} is ignored.
This pragma overrides the effect of the @code{-gnata} switch on the
command line.

@node Pragma Detect_Blocking
@unnumberedsec Pragma Detect_Blocking
@findex Detect_Blocking
@noindent
Syntax:

@smallexample @c ada
pragma Detect_Blocking;
@end smallexample

@noindent
This is a configuration pragma that forces the detection of potentially
blocking operations within a protected operation, and to raise Program_Error
if that happens.

@node Pragma Elaboration_Checks
@unnumberedsec Pragma Elaboration_Checks
@cindex Elaboration control
@findex Elaboration_Checks
@noindent
Syntax:

@smallexample @c ada
pragma Elaboration_Checks (Dynamic | Static);
@end smallexample

@noindent
This is a configuration pragma that provides control over the
elaboration model used by the compilation affected by the
pragma.  If the parameter is @code{Dynamic},
then the dynamic elaboration
model described in the Ada Reference Manual is used, as though
the @code{-gnatE} switch had been specified on the command
line.  If the parameter is @code{Static}, then the default GNAT static
model is used.  This configuration pragma overrides the setting
of the command line.  For full details on the elaboration models
used by the GNAT compiler, see section ``Elaboration Order
Handling in GNAT'' in the @cite{GNAT User's Guide}.

@node Pragma Eliminate
@unnumberedsec Pragma Eliminate
@cindex Elimination of unused subprograms
@findex Eliminate
@noindent
Syntax:

@smallexample @c ada
pragma Eliminate (
    [Unit_Name =>] IDENTIFIER |
                   SELECTED_COMPONENT);

pragma Eliminate (
    [Unit_Name       =>]  IDENTIFIER |
                          SELECTED_COMPONENT,
    [Entity          =>]  IDENTIFIER |
                          SELECTED_COMPONENT |
                          STRING_LITERAL
    [,OVERLOADING_RESOLUTION]);

OVERLOADING_RESOLUTION ::= PARAMETER_AND_RESULT_TYPE_PROFILE |
                           SOURCE_LOCATION

PARAMETER_AND_RESULT_TYPE_PROFILE ::= PROCEDURE_PROFILE |
                                      FUNCTION_PROFILE

PROCEDURE_PROFILE ::= Parameter_Types => PARAMETER_TYPES

FUNCTION_PROFILE ::= [Parameter_Types => PARAMETER_TYPES,]
                      Result_Type => result_SUBTYPE_NAME]

PARAMETER_TYPES ::= (SUBTYPE_NAME @{, SUBTYPE_NAME@})
SUBTYPE_NAME    ::= STRING_VALUE

SOURCE_LOCATION ::= Source_Location => SOURCE_TRACE
SOURCE_TRACE    ::= STRING_VALUE

STRING_VALUE ::= STRING_LITERAL @{& STRING_LITERAL@}
@end smallexample

@noindent
This pragma indicates that the given entity is not used outside the
compilation unit it is defined in. The entity must be an explicitly declared
subprogram; this includes  generic subprogram instances and
subprograms declared in generic package instances.

If the entity to be eliminated is a library level subprogram, then
the first form of pragma @code{Eliminate} is used with only a single argument.
In this form, the @code{Unit_Name} argument specifies the name of the
library  level unit to be eliminated.

In all other cases, both @code{Unit_Name} and @code{Entity} arguments
are required. If item is an entity of a library package, then the first
argument specifies the unit name, and the second argument specifies
the particular entity.  If the second argument is in string form, it must
correspond to the internal manner in which GNAT stores entity names (see