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<H1><a name="Allegrocl_nn1"></a>16 SWIG and Allegro Common Lisp</H1>
<!-- INDEX -->
<div class="sectiontoc">
<ul>
<li><a href="#Allegrocl_nn2">Basics</a>
<ul>
<li><a href="#Allegrocl_nn3">Running Swig</a>
<li><a href="#Allegrocl_nn4">Command Line Options</a>
<li><a href="#Allegrocl_nn5">Inserting user code into generated files</a>
</ul>
<li><a href="#Allegrocl_nn6">Wrapping Overview</a>
<ul>
<li><a href="#Allegrocl_nn7">Function Wrapping</a>
<li><a href="#Allegrocl_nn8">Foreign Wrappers</a>
<li><a href="#Allegrocl_nn9">FFI Wrappers</a>
<li><a href="#Allegrocl_nn10">Non-overloaded Defuns</a>
<li><a href="#Allegrocl_nn11">Overloaded Defuns</a>
<li><a href="#Allegrocl_nn12">What about constant and variable access?</a>
<li><a href="#Allegrocl_nn13">Object Wrapping</a>
</ul>
<li><a href="#Allegrocl_nn14">Wrapping Details</a>
<ul>
<li><a href="#Allegrocl_nn15">Namespaces</a>
<li><a href="#Allegrocl_nn16">Constants</a>
<li><a href="#Allegrocl_nn17">Variables</a>
<li><a href="#Allegrocl_nn18">Enumerations</a>
<li><a href="#Allegrocl_nn19">Arrays</a>
<li><a href="#Allegrocl_nn20">Classes and Structs and Unions (oh my!)</a>
<ul>
<li><a href="#Allegrocl_nn21">CLOS wrapping of</a>
<li><a href="#Allegrocl_nn22">CLOS Inheritance</a>
<li><a href="#Allegrocl_nn23">Member fields and functions</a>
<li><a href="#Allegrocl_nn24">Why not directly access C++ classes using foreign types?</a>
</ul>
<li><a href="#Allegrocl_nn25">Templates</a>
<ul>
<li><a href="#Allegrocl_nn26">Generating wrapper code for templates</a>
<li><a href="#Allegrocl_nn27">Implicit Template instantiation</a>
</ul>
<li><a href="#Allegrocl_nn28">Typedef, Templates, and Synonym Types</a>
<ul>
<li><a href="#Allegrocl_nn29">Choosing a primary type</a>
</ul>
<li><a href="#Allegrocl_nn30">Function overloading/Parameter defaulting</a>
<li><a href="#Allegrocl_nn31">Operator wrapping and Operator overloading</a>
<li><a href="#Allegrocl_nn32">Varargs</a>
<li><a href="#Allegrocl_nn33">C++ Exceptions</a>
<li><a href="#Allegrocl_nn34">Pass by value, pass by reference</a>
</ul>
<li><a href="#Allegrocl_nn35">Typemaps</a>
<ul>
<li><a href="#Allegrocl_nn36">Code Generation in the C++ Wrapper</a>
<ul>
<li><a href="#Allegrocl_nn37">IN Typemap</a>
<li><a href="#Allegrocl_nn38">OUT Typemap</a>
<li><a href="#Allegrocl_nn39">CTYPE Typemap</a>
</ul>
<li><a href="#Allegrocl_nn40">Code generation in Lisp wrappers</a>
<ul>
<li><a href="#Allegrocl_nn41">LIN Typemap</a>
<li><a href="#Allegrocl_nn42">LOUT Typemap</a>
<li><a href="#Allegrocl_nn43">FFITYPE Typemap</a>
<li><a href="#Allegrocl_nn44">LISPTYPE Typemap</a>
<li><a href="#Allegrocl_nn45">LISPCLASS Typemap</a>
</ul>
<li><a href="#Allegrocl_nn46">Modifying SWIG behavior using typemaps</a>
</ul>
<li><a href="#Allegrocl_nn47">Identifier Converter functions</a>
<ul>
<li><a href="#Allegrocl_nn48">Creating symbols in the lisp environment</a>
<li><a href="#Allegrocl_nn49">Existing identifier-converter functions</a>
<ul>
<li><a href="#Allegrocl_nn50">identifier-convert-null</a>
<li><a href="#Allegrocl_nn51">identifier-convert-lispify</a>
<li><a href="#Allegrocl_nn52">Default identifier to symbol conversions</a>
</ul>
<li><a href="#Allegrocl_nn53">Defining your own identifier-converter</a>
<li><a href="#Allegrocl_nn54">Instructing SWIG to use a particular identifier-converter</a>
</ul>
</ul>
</div>
<!-- INDEX -->
<p>
This chapter describes SWIG's support of Allegro Common Lisp. Allegro
CL is a full-featured implementation of the Common Lisp language
standard that includes many vendor-specific enhancements and add-on
modules for increased usability.
</p>
<p>
One such module included in Allegro CL is the Foreign Functions
Interface (FFI). This module, tailored primarily toward interfacing
with C/C++ and, historically, Fortran, provides a means by which
compiled foreign code can be loaded into a running lisp
environment and executed. The interface supports the calling of
foreign functions and methods, allows for executing lisp routines
from foreign code (callbacks), and the passing of data between foreign
and lisp code.
</p>
<p>
The goal of this module is to make it possible to quickly generate the
necessary foreign function definitions so one can make use of C/C++
foreign libraries directly from lisp without the tedium of having to
code them by hand. When necessary, it will also generate further C/C++
code that will need to be linked with the intended library for proper
interfacing from lisp. It has been designed with an eye toward
flexibility. Some foreign function calls may release the heap, while
other should not. Some foreign functions should automatically convert
lisp strings into native strings, while others should not. These
adjustments and many more are possible with the current module.
</p>
<p>
It is significant to note that, while this is a vendor-specific
module, we would like to acknowledge the current and ongoing
work by developers in the open source lisp community that are
working on similar interfaces to implementation-independent
foreign function interfaces (UFFI or CFFI, for example). Such
work can only benefit the lisp community, and we would not
be unhappy to see some enterprising folk use this work to add
to it.
</p>
<H2><a name="Allegrocl_nn2"></a>16.1 Basics</H2>
<H3><a name="Allegrocl_nn3"></a>16.1.1 Running Swig</H3>
<p>
If you're reading this, you must have some library you need to
generate an interface for. In order for SWIG to do this work, however,
it needs a bit of information about how it should go about creating
your interface, and what you are interfacing to.
</p>
<p>
SWIG expects a description of what in the foreign interface you wish
to connect to. It must consisting of C/C++ declarations and special
SWIG directives. SWIG can be furnished with a header file, but an
interface can also be generated without library headers by supplying a
simple text file--called the interface file, which is typically named
with a <tt>.i</tt> extension--containing any foreign declarations of
identifiers you wish to use. The most common approach is to use a an
interface file with directives to parse the needed headers. A straight
parse of library headers will result in usable code, but SWIG
directives provides much freedom in how a user might tailor the
generated code to their needs or style of coding.
</p>
<p>
Note that SWIG does not require any function definitions; the
declarations of those functions is all that is necessary. Be careful
when tuning the interface as it is quite possible to generate code
that will not load or compile.
</p>
<p>
An example interface file is shown below. It makes use of two SWIG
directives, one of which requests that the declarations in a header
file be used to generate part of the interface, and also includes an
additional declaration to be added.</p>
<div class="code">example.i
<pre>
%module example
%include "header.h"
int fact(int n);
</pre>
</div>
<p>The contents of header.h are very simple:</p>
<div class="code">header.h
<pre>
int fact(char *statement); // pass it a fact, and it will rate it.
</pre>
</div>
<p>The contents of example.cl will look like this:</p>
<div class="targetlang">example.cl
<pre>
(defpackage :example
(:use :common-lisp :swig :ff :excl))
... helper routines for defining the interface ...
(swig-in-package ())
(swig-defun ("fact")
((PARM0_statement string (* :char) ))
(:returning (:int )
:strings-convert t)
(let ((SWIG_arg0 PARM0_statement))
(swig-ff-call SWIG_arg0)))
(swig-defun ("fact")
((PARM0_n integer :int ))
(:returning (:int )
:strings-convert t)
(let ((SWIG_arg0 PARM0_n))
(swig-ff-call SWIG_arg0)))
(swig-dispatcher ("fact" :type :function :arities (1)))
</pre>
</div>
<p>
The generated file contains calls to internal swig helper
functions. In this case there are two calls to swig-defun.
These calls will expand into code that will make the appropriate
definitions using the Allegro FFI. Note also, that this code is
<b>erroneous</b>. Function overloading is not supported in C, and this
code will not compile even though SWIG did not complain.
</p>
<p>
In order to generate a C interface to Allegro CL using this code run
swig using the <tt>-allegrocl</tt> option, as below:
</p>
<div class="shell">
<pre>
% swig -allegrocl example.i
</pre>
</div>
<p>
When building an interface to C++ code, include the <tt>-c++</tt> option:
</p>
<div class="shell">
<pre>
% swig -allegrocl -c++ example.i
</pre>
</div>
<p>
As a result of running one of the above commands, a file named <tt>example.cl</tt>
will be generated containing the lisp side of the interface. As well, a file
<tt>example_wrap.cxx</tt> is also generated, containing C/C++ wrapper code to
facilitate access to C++ methods, enumeration values, and constant values.
Wrapper functions are necessary in C++ due to the lack of a standard for mangling
the names of symbols across all C++ compilers. These wrapper functions are
exported from the shared library as appropriate, using the C name mangling
convention. The lisp code that is generated will interface to your foreign
library through these wrappers.
</p>
<p>
It is possible to disable the creation of the .cxx file when generating a C
interface by using the -nocwrap command-line argument. For interfaces that
don't contain complex enum or constant expressions, contain nested struct/union
declarations, or doesn't need to use many of the SWIG customization featuers,
this will result in a more streamlined, direct interface to the
intended module.
</p>
<p>
The generated wrapper file is below. It contains very simple
wrappers by default, that simply pass the arguments to the
actual function.
</p>
<div class="code">example_wrap.i
<pre>
... lots of SWIG internals ...
EXPORT int ACL___fact__SWIG_0 (char *larg1) {
int lresult = (int)0 ;
char *arg1 = (char *) 0 ;
int result;
arg1 = larg1;
try {
result = (int)fact(arg1);
lresult = result;
return lresult;
} catch (...) {
return (int)0;
}
}
EXPORT int ACL___fact__SWIG_1 (int larg1) {
int lresult = (int)0 ;
int arg1 ;
int result;
arg1 = larg1;
try {
result = (int)fact(arg1);
lresult = result;
return lresult;
} catch (...) {
return (int)0;
}
}
</pre>
</div>
<p>
And again, the generated lisp code. Note that it differs from
what is generated when parsing C code:
</p>
<div class="targetlang">
<pre>
...
(swig-in-package ())
(swig-defmethod ("fact" "ACL___fact__SWIG_0" :type :function :arity 1)
((PARM0_statement string (* :char) ))
(:returning (:int )
:strings-convert t)
(let ((SWIG_arg0 PARM0_statement))
(swig-ff-call SWIG_arg0)))
(swig-defmethod ("fact" "ACL___fact__SWIG_1" :type :function :arity 1)
((PARM0_n integer :int ))
(:returning (:int )
:strings-convert t)
(let ((SWIG_arg0 PARM0_n))
(swig-ff-call SWIG_arg0)))
(swig-dispatcher ("fact" :type :function :arities (1)))
</pre>
</div>
<p>In this case, the interface generates two swig-defmethod forms and
a swig-dispatcher form. This provides a single functional interface for
all overloaded routines. A more detailed description of this features
is to be found in the section titled <b>Function overloading/Parameter defaulting</b>.
<p>
In order to load a C++ interface, you will need to build a shared library
from example_wrap.cxx. Be sure to link in the actual library you created
the interface for, as well as any other dependent shared libraries. For
example, if you intend to be able to call back into lisp, you will also
need to link in the Allegro shared library. The library you create from
the C++ wrapper will be what you then load into Allegro CL.
</p>
<H3><a name="Allegrocl_nn4"></a>16.1.2 Command Line Options</H3>
<p>
There are three Allegro CL specific command-line option:
</p>
<div class="shell">
<pre>
swig -allegrocl [ options ] filename
-identifier-converter [name] - Binds the variable swig:*swig-identifier-convert*
in the generated .cl file to <tt>name</tt>.
This function is used to generate symbols
for the lisp side of the interface.
-cwrap - [default] Generate a .cxx file containing C wrapper function when
wrapping C code. The interface generated is similar to what is
done for C++ code.
-nocwrap - Explicitly turn off generation of .cxx wrappers for C code. Reasonable
for modules with simple interfaces. Can not handle all legal enum
and constant constructs, or take advantage of SWIG customization features.
</pre>
</div>
<p>
See <a href="#Allegrocl_nn47">Section 17.5 Identifier converter
functions</a> for more details.
</p>
<H3><a name="Allegrocl_nn5"></a>16.1.3 Inserting user code into generated files</H3>
<p>
It is often necessary to include user-defined code into the
automatically generated interface files. For example, when building
a C++ interface, example_wrap.cxx will likely not compile unless
you add a <tt>#include "header.h"</tt> directive. This can be done
using the SWIG <tt>%insert(section) %{ ...code... %}</tt> directive:
</p>
<div class="code">
<pre>
%module example
%insert("runtime") %{
#include "header.h"
%}
%include "header.h"
int fact(int n);
</pre>
</div>
<p>
Additional sections have been added for inserting into the
generated lisp interface file
</p>
<ul>
<li><tt>lisphead</tt> - inserts before type declarations</li>
<li><tt>lisp</tt> - inserts after type declarations according to
where it appears in the .i file</li>
</ul>
<p>
Note that the block <tt>%{ ... %}</tt> is effectively a shortcut for
<tt>%insert("runtime") %{ ... %}</tt>.
</p>
<H2><a name="Allegrocl_nn6"></a>16.2 Wrapping Overview</H2>
<p>
New users to SWIG are encouraged to read
<a href="SWIG.html#SWIG">SWIG Basics</a>, and
<a href="SWIGPlus.html#SWIGPlus">SWIG and C++</a>, for those
interested in generating an interface to C++.
</p>
<H3><a name="Allegrocl_nn7"></a>16.2.1 Function Wrapping</H3>
<p>
Writing lisp code that directly invokes functions at the foreign
function interface level can be cumbersome. Data must often be
translated between lisp and foreign types, data extracted from
objects, foreign objects allocated and freed upon completion of
the foreign call. Dealing with pointers can be unwieldy when it
comes to keeping them distinct from other valid integer values.
</p>
<p>
We make an attempt to ease some of these burdens by making the
interface to foreign code much more lisp-like, rather than C
like. How this is done is described in later chapters. The
layers themselves, appear as follows:
</p>
<div class="diagram">
<pre>
______________
| | (foreign side)
| Foreign Code | What we're generating an interface to.
|______________|
|
|
_______v______
| | (foreign side)
| Wrapper code | extern "C" wrappers calling C++
|______________| functions and methods.
|
. . . - - + - - . . .
_______v______
| | (lisp side)
| FFI Layer | Low level lisp interface. ff:def-foreign-call,
|______________| ff:def-foreign-variable
|
+----------------------------
_______v______ _______v______
| | | | (lisp side)
| Defuns | | Defmethods | wrapper for overloaded
|______________| |______________| functions or those with
(lisp side) | defaulted arguments
Wrapper for non-overloaded |
functions and methods _______v______
| | (lisp side)
| Defuns | dispatch function
|______________| to overloads based
on arity
</pre>
</div>
<H3><a name="Allegrocl_nn8"></a>16.2.2 Foreign Wrappers</H3>
<p>
These wrappers are as generated by SWIG default. The types of
function parameters can be transformed in place using the CTYPE
typemap. This is use for converting pass-by-value parameters to
pass-by-reference where necessary. All wrapper parameters are then
bound to local variables for possible transformation of values
(see LIN typemap). Return values can be transformed via the OUT
typemap.
</p>
<H3><a name="Allegrocl_nn9"></a>16.2.3 FFI Wrappers</H3>
<p>
These are the generated ff:def-foreign-call forms. No typemaps are
applicable to this layer, but the <tt>%ffargs</tt> directive is
available for use in .i files, to specify which keyword arguments
should be specified for a given function.
</p>
<div class="code">ffargs.i:
<pre>
%module ffargs
%ffargs(strings_convert="nil",call_direct="t") foo;
%ffargs(strings_convert="nil",release_heap=":never",optimize_for_space="t") bar;
int foo(float f1, float f2);
int foo(float f1, char c2);
void bar(void *lisp_fn);
char *xxx();
</pre>
</div>
<p>Generates:
</p>
<div class="targetlang">ffargs.cl:
<pre>
(swig-in-package ())
(swig-defmethod ("foo" "ACL___foo__SWIG_0" :type :function :arity 2)
((PARM0_f1 single-float :float )
(PARM1_f2 single-float :float ))
(:returning (:int )
:call-direct t
:strings-convert nil)
(let ((SWIG_arg0 PARM0_f1))
(let ((SWIG_arg1 PARM1_f2))
(swig-ff-call SWIG_arg0 SWIG_arg1))))
(swig-defmethod ("foo" "ACL___foo__SWIG_1" :type :function :arity 2)
((PARM0_f1 single-float :float )
(PARM1_c2 character :char character))
(:returning (:int )
:call-direct t
:strings-convert nil)
(let ((SWIG_arg0 PARM0_f1))
(let ((SWIG_arg1 PARM1_c2))
(swig-ff-call SWIG_arg0 SWIG_arg1))))
(swig-dispatcher ("foo" :type :function :arities (2)))
(swig-defun ("bar" "ACL___bar__SWIG_0" :type :function)
((PARM0_lisp_fn (* :void) ))
(:returning (:void )
:release-heap :never
:optimize-for-space t
:strings-convert nil)
(let ((SWIG_arg0 PARM0_lisp_fn))
(swig-ff-call SWIG_arg0)))
(swig-defun ("xxx" "ACL___xxx__SWIG_0" :type :function)
(:void)
(:returning ((* :char) )
:strings-convert t)
(swig-ff-call))
</pre>
</div>
<div class="code">
<pre>%ffargs(strings_convert="t");</pre>
</div>
<p>
Is the only default value specified in <tt>allegrocl.swg</tt> to force
the muffling of warnings about automatic string conversion when defining
ff:def-foreign-call's.
</p>
<H3><a name="Allegrocl_nn10"></a>16.2.4 Non-overloaded Defuns</H3>
<p>
These are simple defuns. There is no typechecking of arguments.
Parameters are bound to local variables for possible
transformation of values, such as pulling values out of instance
slots or allocating temporary stack allocated structures, via the
<tt>lin</tt> typemap. These arguments are then passed to the
foreign-call (where typechecking may occur). The return value from
this function can be manipulated via the <tt>lout</tt> typemap.
</p>
<H3><a name="Allegrocl_nn11"></a>16.2.5 Overloaded Defuns</H3>
<p>
In the case of overloaded functions, mulitple layers are
generated. First, all the overloads for a given name are separated
out into groups based on arity, and are wrapped in
defmethods. Each method calls a distinct wrapper function, but are
themselves distinguished by the types of their arguments
(see <tt>lispclass</tt> typemap). These are further wrapped in a
dispatching function (defun) which will invoke the appropriate
generic-function based on arity. This provides a single functional
interface to all overloads. The return value from this function
can be manipulated via the <tt>lout</tt> typemap.
</p>
<H3><a name="Allegrocl_nn12"></a>16.2.6 What about constant and variable access?</H3>
<p>
Along with the described functional layering, when creating a .cxx wrapper,
this module will generate getter and--if not immutable--setter,
functions for variables and constants. If the -nocwrap option is used,
<tt>defconstant</tt> and <tt>ff:def-foreign-variable</tt> forms will be
generated for accessing constants and global variables. These, along with
the <tt>defuns</tt> listed above are the intended API for calling
into the foreign module.
</p>
<H3><a name="Allegrocl_nn13"></a>16.2.7 Object Wrapping</H3>
<p>
All non-primitive types (Classes, structs, unions, and typedefs
involving same) have a corresponding foreign-type defined on the
lisp side via ff:def-foreign-type.
</p>
<p>
All non-primitive types are further represented by a CLOS class,
created via defclass. An attempt is made to create the same class
hierarchy, with all classes inheriting directly or indirectly from
ff:foreign-pointer. Further, wherever it is apparent, all pointers
returned from foreign code are wrapped in a CLOS instance of the
appropriate class. For ff:def-foreign-calls that have been defined
to expect a :foreign-address type as argument, these CLOS instances
can legally be passed and the pointer to the C++ object
automatically extracted. This is a natural feature of Allegro's
foreign function interface.
</p>
<H2><a name="Allegrocl_nn14"></a>16.3 Wrapping Details</H2>
<p>
In this section is described how particular C/C++ constructs are
translated into lisp.
</p>
<H3><a name="Allegrocl_nn15"></a>16.3.1 Namespaces</H3>
<p>
C++ namespaces are translated into Lisp packages by SWIG. The
Global namespace is mapped to a package named by the <tt>%module</tt>
directive or the <tt>-module</tt> command-line argument. Further
namespaces are created using Allegro CLs nested namespace convention.
For example:
</p>
<div class="code">foo.i:
<pre>
%module foo
%{
#include "foo.h"
%}
%include "foo.h"
namespace car {
...
namespace tires {
int do_something(int n);
}
}
</pre>
</div>
<p>Generates the following code.
</p>
<div class="targetlang">foo.cl
<pre>
(defpackage :foo
(:use :common-lisp :swig :ff :excl))
...
(swig-defpackage ("car"))
(swig-defpackage ("car" "tires"))
...
(swig-in-package ("car" "tires"))
(swig-defun ("do_something" "ACL_car_tires__do_something__SWIG_0" :type :function)
((PARM0_n :int ))
(:returning (:int )
:strings-convert t)
(let ((SWIG_arg0 PARM0_n))
(swig-ff-call SWIG_arg0)))
</pre>
</div>
<p>
The above interface file would cause packages foo, foo.car, and
foo.car.tires to be created. One would find the function wrapper
for do_something defined in the foo.car.tires package(*).
</p>
<p>(<b>*</b>) Except for the package named by the module, all
namespace names are passed to the identifier-converter-function
as strings with a <tt>:type</tt> of <tt>:namespace</tt>. It is the
job of this function to generate the desired symbol, accounting for
case preferences, additional naming cues, etc.
</p>
<H3><a name="Allegrocl_nn16"></a>16.3.2 Constants</H3>
<p>
Constants, as declared by the preprocessor #define macro or SWIG
<tt>%constant</tt> directive, are included in SWIGs parse tree
when it can be determined that they are, or could be reduced to,
a literal value. Such values are translated into defconstant
forms in the generated lisp wrapper when the -nocwrap command-line
options is used. Else, wrapper functions are generated as in the
case of variable access (see section below).
</p>
<p>
Here are examples of simple preprocessor constants when using -nocwrap.
</p>
<div class="code">
<pre>
#define A 1 => (swig-defconstant "A" 1)
#define B 'c' => (swig-defconstant "B" #\c)
#define C B => (swig-defconstant "C" #\c)
#define D 1.0e2 => (swig-defconstant "D" 1.0d2)
#define E 2222 => (swig-defconstant "E" 2222)
#define F (unsigned int)2222 => no code generated
#define G 1.02e2f => (swig-defconstant "G" 1.02f2)
#define H foo => no code generated
</pre>
</div>
<p>
Note that where SWIG is unable to determine if a constant is
a literal, no node is added to the SWIG parse tree, and so
no values can be generated.
</p>
<p>
For preprocessor constants containing expressions which can be
reduced to literal values, nodes are created, but with no simplification
of the constant value. A very very simple infix to prefix converter
has been implemented that tries to do the right thing for simple cases, but
does not for more complex expressoins. If the literal parser determines
that something is wrong, a warning will be generated and the literal
expression will be included in the generated code, but commented out.
</p>
<div class="code">
<pre>
#define I A + E => (swig-defconstant "I" (+ 1 2222))
#define J 1|2 => (swig-defconstant "J" (logior 1 2))
#define Y 1 + 2 * 3 + 4 => (swig-defconstant "Y" (* (+ 1 2) (+ 3 4)))
#define Y1 (1 + 2) * (3 + 4) => (swig-defconstant "Y1" (* (+ 1 2) (+ 3 4)))
#define Y2 1 * 2 + 3 * 4 => (swig-defconstant "Y2" (* 1 (+ 2 3) 4)) ;; WRONG
#define Y3 (1 * 2) + (3 * 4) => (swig-defconstant "Y3" (* 1 (+ 2 3) 4)) ;; WRONG
#define Z 1 + 2 - 3 + 4 * 5 => (swig-defconstant "Z" (* (+ 1 (- 2 3) 4) 5)) ;; WRONG
</pre>
</div>
<p>
Users are cautioned to get to know their constants before use.
</p>
<H3><a name="Allegrocl_nn17"></a>16.3.3 Variables</H3>
<p>
For C wrapping, a def-foreign-variable call is generated for access
to global variables.
</p>
<p>
When wrapping C++ code, both global and member variables, getter
wrappers are generated for accessing their value, and if not immutable,
setter wrappers as well. In the example below, note the lack of a
setter wrapper for global_var, defined as const.
</p>
<div class="code">vars.h
<pre>
namespace nnn {
int const global_var = 2;
float glob_float = 2.0;
}
</pre>
</div>
<p>
Generated code:
</p>
<div class="targetlang">vars.cl
<pre>
(swig-in-package ("nnn"))
(swig-defun ("global_var" "ACL_nnn__global_var_get__SWIG_0" :type :getter)
(:void)
(:returning (:int )
:strings-convert t)
(swig-ff-call))
(swig-defun ("glob_float" "ACL_nnn__glob_float_set__SWIG_0" :type :setter)
((PARM0_glob_float :float ))
(:returning (:void )
:strings-convert t)
(let ((SWIG_arg0 PARM0_glob_float))
(swig-ff-call SWIG_arg0)))
(swig-defun ("glob_float" "ACL_nnn__glob_float_get__SWIG_0" :type :getter)
(:void)
(:returning (:float )
:strings-convert t)
(swig-ff-call))
</pre>
</div>
<p>
Note also, that where applicable, setter wrappers are implemented
as setf methods on the getter function, providing a lispy interface
to the foreign code.
</p>
<div class="targetlang">
<pre>
user> (load "globalvar.dll")
; Foreign loading globalvar.dll.
t
user> (load "globalvar.cl")
; Loading c:\mikel\src\swig\test\globalvar.cl
t
user>
globalvar> (globalvar.nnn::global_var)
2
globalvar> (globalvar.nnn::glob_float)
2.0
globalvar> (setf (globalvar.nnn::glob_float) 3.0)
3.0
globalvar> (globalvar.nnn::glob_float)
3.0
</pre>
</div>
<H3><a name="Allegrocl_nn18"></a>16.3.4 Enumerations</H3>
<p>
In C, an enumeration value is an integer value, while in C++ an
enumeration value is implicitly convertible to an integer value,
but can also be distinguished by it's enum type. For each enum
declaration a def-foreign-type is generated, assigning the enum
a default type of :int. Users may adjust the foreign type of
enums via SWIG <tt>typemaps</tt>.
</p>
<p>
Enum values are a bit trickier as they can be initialized using
any valid C/C++ expression. In C with the -nocwrap command-line option,
we handle the typical cases (simple integer initialization) and
generate a defconstant form for each enum value. This has the advantage
of it not being necessary to probe into foreign space to retrieve enum
values. When generating a .cxx wrapper file, a more general solution is
employed. A wrapper variable is created in the module_wrap.cxx file, and
a ff:def-foreign-variable call is generated to retrieve it's value into lisp.
</p>
<p>For example, the following header file
<div class="code">enum.h:
<pre>
enum COL { RED, GREEN, BLUE };
enum FOO { FOO1 = 10, FOO2, FOO3 };
</pre>
</div>
<p>
In -nocwrap mode, generates
</p>
<div class="targetlang">enum.cl:
<pre>
(swig-def-foreign-type "COL" :int)
(swig-defconstant "RED" 0)
(swig-defconstant "GREEN" (+ #.(swig-insert-id "RED" () :type :constant) 1))
(swig-defconstant "BLUE" (+ #.(swig-insert-id "GREEN" () :type :constant) 1))
(swig-def-foreign-type "FOO" :int)
(swig-defconstant "FOO1" 10)
(swig-defconstant "FOO2" (+ #.(swig-insert-id "FOO1" () :type :constant) 1))
(swig-defconstant "FOO3" (+ #.(swig-insert-id "FOO2" () :type :constant) 1))
</pre>
</div>
<p>And when generating a .cxx wrapper
<div class="code">enum_wrap.cxx:
<pre>
EXPORT const int ACL_ENUM___RED__SWIG_0 = RED;
EXPORT const int ACL_ENUM___GREEN__SWIG_0 = GREEN;
EXPORT const int ACL_ENUM___BLUE__SWIG_0 = BLUE;
EXPORT const int ACL_ENUM___FOO1__SWIG_0 = FOO1;
EXPORT const int ACL_ENUM___FOO2__SWIG_0 = FOO2;
EXPORT const int ACL_ENUM___FOO3__SWIG_0 = FOO3;
</pre>
</div>
<p>
and
</p>
<div class="targetlang">enum.cl:
<pre>
(swig-def-foreign-type "COL" :int)
(swig-defvar "RED" "ACL_ENUM___RED__SWIG_0" :type :constant)
(swig-defvar "GREEN" "ACL_ENUM___GREEN__SWIG_0" :type :constant)
(swig-defvar "BLUE" "ACL_ENUM___BLUE__SWIG_0" :type :constant)
(swig-def-foreign-type "FOO" :int)
(swig-defvar "FOO1" "ACL_ENUM___FOO1__SWIG_0" :type :constant)
(swig-defvar "FOO2" "ACL_ENUM___FOO2__SWIG_0" :type :constant)
(swig-defvar "FOO3" "ACL_ENUM___FOO3__SWIG_0" :type :constant)
</pre>
</div>
<H3><a name="Allegrocl_nn19"></a>16.3.5 Arrays</H3>
<p>
One limitation in the Allegro CL foreign-types module, is that,
without macrology, expressions may not be used to specify the
dimensions of an array declaration. This is not a horrible
drawback unless it is necessary to allocate foreign structures
based on the array declaration using ff:allocate-fobject. When it
can be determined that an array bound is a valid numeric value,
SWIG will include this in the generated array declaration on the
lisp side, otherwise the value will be included, but commented out.
</p>
<p>
Below is a comprehensive example, showing a number of legal
C/C++ array declarations and how they are translated
into foreign-type specifications in the generated lisp code.
</p>
<div class="code">array.h
<pre>
#define MAX_BUF_SIZE 1024
namespace FOO {
int global_var1[13];
float global_var2[MAX_BUF_SIZE];
}
enum COLOR { RED = 10, GREEN = 20, BLUE, PURPLE = 50, CYAN };
namespace BAR {
char global_var3[MAX_BUF_SIZE + 1];
float global_var4[MAX_BUF_SIZE][13];
signed short global_var5[MAX_BUF_SIZE + MAX_BUF_SIZE];
int enum_var5[GREEN];
int enum_var6[CYAN];
COLOR enum_var7[CYAN][MAX_BUF_SIZE];
}
</pre>
</div>
<p>
Generates:
</p>
<div class="targetlang">array.cl
<pre>
(in-package #.*swig-module-name*)
(swig-defpackage ("FOO"))
(swig-defpackage ("BAR"))
(swig-in-package ())
(swig-def-foreign-type "COLOR" :int)
(swig-defvar "RED" "ACL_ENUM___RED__SWIG_0" :type :constant)
(swig-defvar "GREEN" "ACL_ENUM___GREEN__SWIG_0" :type :constant)
(swig-defvar "BLUE" "ACL_ENUM___BLUE__SWIG_0" :type :constant)
(swig-defvar "PURPLE" "ACL_ENUM___PURPLE__SWIG_0" :type :constant)
(swig-defvar "CYAN" "ACL_ENUM___CYAN__SWIG_0" :type :constant)
(swig-in-package ())
(swig-defconstant "MAX_BUF_SIZE" 1024)
(swig-in-package ("FOO"))
(swig-defun ("global_var1" "ACL_FOO__global_var1_get__SWIG_0" :type :getter)
(:void)
(:returning ((* :int) )
:strings-convert t)
(make-instance 'ff:foreign-pointer :foreign-address (swig-ff-call)))
(swig-defun ("global_var2" "ACL_FOO__global_var2_set__SWIG_0" :type :setter)
((global_var2 (:array :float 1024) ))
(:returning (:void )
:strings-convert t)
(let ((SWIG_arg0 global_var2))
(swig-ff-call SWIG_arg0)))
(swig-in-package ())
(swig-in-package ("BAR"))
(swig-defun ("global_var3" "ACL_BAR__global_var3_set__SWIG_0" :type :setter)
((global_var3 (:array :char #|1024+1|#) ))
(:returning (:void )
:strings-convert t)
(let ((SWIG_arg0 global_var3))
(swig-ff-call SWIG_arg0)))
(swig-defun ("global_var4" "ACL_BAR__global_var4_set__SWIG_0" :type :setter)
((global_var4 (:array (:array :float 13) 1024) ))
(:returning (:void )
:strings-convert t)
(let ((SWIG_arg0 global_var4))
(swig-ff-call SWIG_arg0)))
(swig-defun ("global_var4" "ACL_BAR__global_var4_get__SWIG_0" :type :getter)
(:void)
(:returning ((* (:array :float 13)) )
:strings-convert t)
(make-instance 'ff:foreign-pointer :foreign-address (swig-ff-call)))
(swig-defun ("global_var5" "ACL_BAR__global_var5_set__SWIG_0" :type :setter)
((global_var5 (:array :short #|1024+1024|#) ))
(:returning (:void )
:strings-convert t)
(let ((SWIG_arg0 global_var5))
(swig-ff-call SWIG_arg0)))
(swig-defun ("enum_var5" "ACL_BAR__enum_var5_set__SWIG_0" :type :setter)
((enum_var5 (:array :int #|GREEN|#) ))
(:returning (:void )
:strings-convert t)
(let ((SWIG_arg0 enum_var5))
(swig-ff-call SWIG_arg0)))
(swig-defun ("enum_var6" "ACL_BAR__enum_var6_set__SWIG_0" :type :setter)
((enum_var6 (:array :int #|CYAN|#) ))
(:returning (:void )
:strings-convert t)
(let ((SWIG_arg0 enum_var6))
(swig-ff-call SWIG_arg0)))
(swig-defun ("enum_var7" "ACL_BAR__enum_var7_set__SWIG_0" :type :setter)
((enum_var7 (:array (:array #.(swig-insert-id "COLOR" ()) 1024) #|CYAN|#) ))
(:returning (:void )
:strings-convert t)
(let ((SWIG_arg0 enum_var7))
(swig-ff-call SWIG_arg0)))
(swig-defun ("enum_var7" "ACL_BAR__enum_var7_get__SWIG_0" :type :getter)
(:void)
(:returning ((* (:array #.(swig-insert-id "COLOR" ()) 1024)) )
:strings-convert t)
(make-instance 'ff:foreign-pointer :foreign-address (swig-ff-call)))
</pre>
</div>
<H3><a name="Allegrocl_nn20"></a>16.3.6 Classes and Structs and Unions (oh my!)</H3>
<H4><a name="Allegrocl_nn21"></a>16.3.6.1 CLOS wrapping of</H4>
<p>
Classes, unions, and structs are all treated the same way by the
interface generator. For any of these objects, a
def-foreign-type and a defclass form are generated. For every
function that returns an object (or pointer/reference) of C/C++
type <tt>X</tt>, the wrapping defun (or defmethod) on the Lisp
side will automatically wrap the pointer returned in an instance
of the apropriate class. This makes it much easier to write and
debug code than if pointers were passed around as a jumble of
integer values.
</p>
<H4><a name="Allegrocl_nn22"></a>16.3.6.2 CLOS Inheritance</H4>
<p>
The CLOS class schema generated by the interface mirrors the
inheritance of the classes in foreign code, with the
ff:foreign-pointer class at its root. ff:foreign-pointer is a thin
wrapper for pointers that is made available by the foreign function
interface. It's key benefit is that it may be passed as an argument
to any ff:def-foreign-call that is expecting a pointer as the
parameter.
</p>
<H4><a name="Allegrocl_nn23"></a>16.3.6.3 Member fields and functions</H4>
<p>
All public fields will have accessor getter/setter functions
generated for them, as appropriate. All public member functions
will have wrapper functions generated.
</p>
<p>
We currently ignore anything that isn't <tt>public</tt> (i.e.
<tt>private</tt> or <tt>protected</tt>), because the C++ compiler
won't allow the wrapper functions to access such fields. Likewise,
the interface does nothing for <tt>friend</tt> directives,
</p>
<H4><a name="Allegrocl_nn24"></a>16.3.6.4 Why not directly access C++ classes using foreign types?</H4>
<p>
The def-foreign-type generated by the SWIG interface is
currently incomplete. We can reliably generate the object layout
of simple structs and unions; they can be allocated via
ff:allocate-fobject, and their member variables accessed
directly using the various ff:fslot-value-* functions. However,
the layout of C++ classes is more complicated. Different
compilers adjust class layout based on inheritance patterns, and
the presence of virtual member functions. The size of member
function pointers vary across compilers as well. As a result, it
is recommended that users of any generated interface not attempt
to access C++ instances via the foreign type system, but instead
use the more robust wrapper functions.
</p>
<H3><a name="Allegrocl_nn25"></a>16.3.7 Templates</H3>
<H4><a name="Allegrocl_nn26"></a>16.3.7.1 Generating wrapper code for templates</H4>
<p>
SWIG provides support for dealing with templates, but by
default, it will not generate any member variable or function
wrappers for templated classes. In order to create these
wrappers, you need to explicitly tell SWIG to instantiate
them. This is done via the
<a href="SWIGPlus.html#SWIGPlus_nn30"><tt>%template</tt></a>
directive.
</p>
<H4><a name="Allegrocl_nn27"></a>16.3.7.2 Implicit Template instantiation</H4>
<p>
While no wrapper code is generated for accessing member
variables, or calling member functions, type code is generated
to include these templated classes in the foreign-type and CLOS
class schema.
</p>
<H3><a name="Allegrocl_nn28"></a>16.3.8 Typedef, Templates, and Synonym Types</H3>
<p>
In C/C++ it is possible, via typedef, to have many names refer to
the same <tt>type</tt>. In general, this is not a problem, though
it can lead to confusion. Assume the below C++ header file:
</p>
<div class="code">synonyms.h
<pre>
class A {
int x;
int y;
};
typedef A Foo;
A *xxx(int i); /* sets A->x = A->y = i */
Foo *yyy(int i); /* sets Foo->x = Foo->y = i */
int zzz(A *inst = 0); /* return inst->x + inst->y */
</pre>
</div>
<p>
The function <tt>zzz</tt> is an overloaded functions; the
foreign function call to it will be wrapped in a
generic-function whose argument will be checked against a type
of <tt>A</tt>. Assuming a simple implementation, a call
to <tt>xxx(1)</tt> will return a pointer to an A object, which
will be wrapped in a CLOS instance of class <tt>A</tt>, and a
call to <tt>yyy(1)</tt> will result in a CLOS instance of
type <tt>Foo</tt> being returned. Without establishing a clear
type relationship between <tt>Foo</tt> and <tt>A</tt>, an
attempt to call <tt>zzz(yyy(1))</tt> will result in an error.
</p>
<p>
We resolve this issue, by noting synonym relationships between
types while generating the interface. A Primary type is selected
(more on this below) from the candidate list of synonyms. For
all other synonyms, intead of generating a distinct CLOS class
definition, we generate a form that expands to:
</p>
<div class="targetlang">
<tt>(setf (find-class <synonym>) <primary>)</tt>
</div>
<p>
The result is that all references to synonym types in foreign
code, are wrapped in the same CLOS wrapper, and, in particular,
method specialization in wrapping generic functions works as
expected.
</p>
<p>
Given the above header file, synonym.h, a Lisp session would
appear as follows:
</p>
<div class="targetlang">
<pre>
CL-USER> (load "synonym.dll")
; Foreign loading synonym.dll.
t
CL-USER> (load "synonym.cl")
; Loading c:\mikel\src\swig\test\synonym.cl
t
CL-USER>
synonym> (setf a (xxx 3))
#<A nil #x3261a0 @ #x207299da>
synonym> (setf foo (yyy 10))
#<A nil #x3291d0 @ #x2072e982>
synonym> (zzz a)
6
synonym> (zzz foo)
20
synonym>
</pre>
</div>
<H4><a name="Allegrocl_nn29"></a>16.3.8.1 Choosing a primary type</H4>
<p>
The choice of a primary type is selected by the following
criteria from a set of synonym types.
</p>
<ul>
<li>
If a synonym type has a class definition, it is the primary type.
</li>
<li>
If a synonym type is a class template and has been explicitly
instantiated via <tt>%template</tt>, it is the primary type.
</li>
<li>
For all other sets of synonymous types, the synonym which is
parsed first becomes the primary type.
</li>
</ul>
<H3><a name="Allegrocl_nn30"></a>16.3.9 Function overloading/Parameter defaulting</H3>
<p>
For each possible argument combination, a distinct wrapper
function is created in the .cxx file. On the Lisp side, a
generic functions is defined for each possible arity the
overloaded/defaulted call may have. Each distinct wrapper is
then called from within a defmethod on the appropriate generic
function. These are further wrapped inside a dispatch function
that checks the number of arguments it is called with and passes
them via apply to the appropriate generic-function. This allows
for a single entry point to overloaded functions on the lisp
side.
</p>
<p>Example:
</p>
<div class="code">overload.h:
<pre>
class A {
public:
int x;
int y;
};
float xxx(int i, int x = 0); /* return i * x */
float xxx(A *inst, int x); /* return x + A->x + A->y */
</pre>
</div>
<p>Creates the following three wrappers, for each of the possible argument
combinations
</p>
<div class="code">overload_wrap.cxx
<pre>
EXPORT void ACL___delete_A__SWIG_0 (A *larg1) {
A *arg1 = (A *) 0 ;
arg1 = larg1;
try {
delete arg1;
} catch (...) {
}
}
EXPORT float ACL___xxx__SWIG_0 (int larg1, int larg2) {
float lresult = (float)0 ;
int arg1 ;
int arg2 ;
float result;
arg1 = larg1;
arg2 = larg2;
try {
result = (float)xxx(arg1,arg2);
lresult = result;
return lresult;
} catch (...) {
return (float)0;
}
}
EXPORT float ACL___xxx__SWIG_1 (int larg1) {
float lresult = (float)0 ;
int arg1 ;
float result;
arg1 = larg1;
try {
result = (float)xxx(arg1);
lresult = result;
return lresult;
} catch (...) {
return (float)0;
}
}
EXPORT float ACL___xxx__SWIG_2 (A *larg1, int larg2) {
float lresult = (float)0 ;
A *arg1 = (A *) 0 ;
int arg2 ;
float result;
arg1 = larg1;
arg2 = larg2;
try {
result = (float)xxx(arg1,arg2);
lresult = result;
return lresult;
} catch (...) {
return (float)0;
}
}
</pre>
</div>
<p>
And the following foreign-function-call and method definitions on the
lisp side:
</p>
<div class="targetlang">overload.cl
<pre>
(swig-defmethod ("xxx" "ACL___xxx__SWIG_0" :type :function :arity 2)
((PARM0_i integer :int )
(PARM1_x integer :int ))
(:returning (:float )
:strings-convert t)
(let ((SWIG_arg0 PARM0_i))
(let ((SWIG_arg1 PARM1_x))
(swig-ff-call SWIG_arg0 SWIG_arg1))))
(swig-defmethod ("xxx" "ACL___xxx__SWIG_1" :type :function :arity 1)
((PARM0_i integer :int ))
(:returning (:float )
:strings-convert t)
(let ((SWIG_arg0 PARM0_i))
(swig-ff-call SWIG_arg0)))
(swig-defmethod ("xxx" "ACL___xxx__SWIG_2" :type :function :arity 2)
((PARM0_inst #.(swig-insert-id "A" () :type :class) (* #.(swig-insert-id "A" ())) )
(PARM1_x integer :int ))
(:returning (:float )
:strings-convert t)
(let ((SWIG_arg0 PARM0_inst))
(let ((SWIG_arg1 PARM1_x))
(swig-ff-call SWIG_arg0 SWIG_arg1))))
(swig-dispatcher ("xxx" :type :function :arities (1 2)))
</pre>
</div>
<p>And their usage in a sample lisp session:
</p>
<div class="targetlang">
<pre>
overload> (setf a (new_A))
#<A nil #x329268 @ #x206cf612>
overload> (setf (A_x a) 10)
10
overload> (setf (A_y a) 20)
20
overload> (xxx 1)
0.0
overload> (xxx 3 10)
30.0
overload> (xxx a 1)
31.0
overload> (xxx a 2)
32.0
overload>
</pre>
</div>
<H3><a name="Allegrocl_nn31"></a>16.3.10 Operator wrapping and Operator overloading</H3>
<p>
Wrappers to defined C++ Operators are automatically renamed, using
<tt>%rename</tt>, to the following defaults:
</p>
<div class="code">
<pre>
/* name conversion for overloaded operators. */
#ifdef __cplusplus
%rename(__add__) *::operator+;
%rename(__pos__) *::operator+();
%rename(__pos__) *::operator+() const;
%rename(__sub__) *::operator-;
%rename(__neg__) *::operator-() const;
%rename(__neg__) *::operator-();
%rename(__mul__) *::operator*;
%rename(__deref__) *::operator*();
%rename(__deref__) *::operator*() const;
%rename(__div__) *::operator/;
%rename(__mod__) *::operator%;
%rename(__logxor__) *::operator^;
%rename(__logand__) *::operator&;
%rename(__logior__) *::operator|;
%rename(__lognot__) *::operator~();
%rename(__lognot__) *::operator~() const;
%rename(__not__) *::operator!();
%rename(__not__) *::operator!() const;
%rename(__assign__) *::operator=;
%rename(__add_assign__) *::operator+=;
%rename(__sub_assign__) *::operator-=;
%rename(__mul_assign__) *::operator*=;
%rename(__div_assign__) *::operator/=;
%rename(__mod_assign__) *::operator%=;
%rename(__logxor_assign__) *::operator^=;
%rename(__logand_assign__) *::operator&=;
%rename(__logior_assign__) *::operator|=;
%rename(__lshift__) *::operator<<;
%rename(__lshift_assign__) *::operator<<=;
%rename(__rshift__) *::operator>>;
%rename(__rshift_assign__) *::operator>>=;
%rename(__eq__) *::operator==;
%rename(__ne__) *::operator!=;
%rename(__lt__) *::operator<;
%rename(__gt__) *::operator>;
%rename(__lte__) *::operator<=;
%rename(__gte__) *::operator>=;
%rename(__and__) *::operator&&;
%rename(__or__) *::operator||;
%rename(__preincr__) *::operator++();
%rename(__postincr__) *::operator++(int);
%rename(__predecr__) *::operator--();
%rename(__postdecr__) *::operator--(int);
%rename(__comma__) *::operator,();
%rename(__comma__) *::operator,() const;
%rename(__member_ref__) *::operator->;
%rename(__member_func_ref__) *::operator->*;
%rename(__funcall__) *::operator();
%rename(__aref__) *::operator[];
</pre>
</div>
<p>
Name mangling occurs on all such renamed identifiers, so that wrapper name
generated by <tt>B::operator=</tt> will be <tt>B___eq__</tt>, i.e.
<tt><class-or-namespace>_</tt> has been added. Users may modify
these default names by adding <tt>%rename</tt> directives in their own .i files.
</p>
<p>
Operator overloading can be achieved by adding functions based
on the mangled names of the function. In the following example,
a class B is defined with a Operator== method defined. The
swig <tt>%extend</tt> directive is used to add an overload method
on Operator==.
</p>
<div class="code">opoverload.h
<pre>
class B {
public:
int x;
int y;
bool operator==(B const& other) const;
};
</pre>
</div>
<p>
and
</p>
<div class="code">opoverload.i
<pre>
%module opoverload
%{
#include <fstream>
#include "opoverload.h"
%}
%{
bool B___eq__(B const *inst, int const x)
{
// insert the function definition into the wrapper code before
// the wrapper for it.
// ... do stuff ...
}
%}
%include "opoverload.h"
%extend B {
public:
bool __eq__(int const x) const;
};
</pre>
</div>
<p>
Either operator can be called via a single call
to the dispatch function:
</p>
<div class="targetlang">
<pre>
opoverload> (B___eq__ x1 x2)
nil
opoverload> (B___eq__ x1 3)
nil
opoverload>
</pre>
</div>
<H3><a name="Allegrocl_nn32"></a>16.3.11 Varargs</H3>
<p>
Variable length argument lists are not supported, by default. If
such a function is encountered, a warning will generated to
stderr. Varargs are supported via the SWIG <tt>%vararg</tt>
directive. This directive allows you to specify a (finite)
argument list which will be inserted into the wrapper in place
of the variable length argument indicator. As an example,
consider the function <tt>printf()</tt>. It's declaration would
appear as follows:
</p>
<p>
See the following section
on <a href="Varargs.html#Varargs">Variable Length arguments</a>
provides examples on how <tt>%vararg</tt> can be used, along
with other ways such functions can be wrapped.
</p>
<H3><a name="Allegrocl_nn33"></a>16.3.12 C++ Exceptions</H3>
<p>
Each C++ wrapper includes a handler to catch any exceptions that may
be thrown while in foreign code. This helps prevent simple C++ errors
from killing the entire lisp process. There is currently no mechanism
to have these exceptions forwarded to the lisp condition system, nor
has any explicit support of the exception related SWIG typemaps been
implemented.
</p>
<H3><a name="Allegrocl_nn34"></a>16.3.13 Pass by value, pass by reference</H3>
<p>
Allegro CL does not support the passing of non-primitive foreign
structures by value. As a result, SWIG must automatically detect
and convert function parameters and return values to pointers
whenever necessary. This is done via the use of <tt>typemaps</tt>,
and should not require any fine tuning by the user, even for
newly defined types.
</p>
<H2><a name="Allegrocl_nn35"></a>16.4 Typemaps</H2>
<p>
SWIG Typemaps provide a powerful tool for automatically generating
code to handle various menial tasks required of writing an interface
to foreign code. The purpose of this section is to describe each of
the typemaps used by the Allegro CL module. Please read the chapter
on <a href="Typemaps.html#Typemaps">Typemaps</a> for more information.
</p>
<H3><a name="Allegrocl_nn36"></a>16.4.1 Code Generation in the C++ Wrapper</H3>
<p>
Every C++ wrapper generated by SWIG takes the following form:
</p>
<div class="diagram">
<pre>
return-val wrapper-name(parm0, parm1, ..., parmN)
{
return-val lresult; /* return value from wrapper */
<local-declaration>
... results; /* return value from function call */
<binding locals to parameters>
try {
result = function-name(local0, local1, ..., localN);
<convert and bind result to lresult>
return lresult;
catch (...) {
return (int)0;
}
</pre>
</div>
<H4><a name="Allegrocl_nn37"></a>16.4.1.1 IN Typemap</H4>
<p>
the <tt>in</tt> typemap is used to generate code to convert parameters
passed to C++ wrapper functions into the arguments desired for the
call being wrapped. That is, it fills in the code for the
<tt><binding locals to parameters></tt> section above. We
use this map to automatically convert parameters passed by
reference to the wrapper function into by-value arguments for
the wrapped call, and also to convert boolean values, which are
passed as integers from lisp (by default), into the appropriate
type for the language of code being wrapped.
</p>
<p>These are the default specifications for the IN typemap. Here,
<tt>$input</tt> refers to the parameter code is being generated
for, and <tt>$1</tt> is the local variable to which it is
being assigned. The default settings of this typemap are as follows:
</p>
<div class="code">
<pre>
%typemap(in) bool "$1 = (bool)$input;";
%typemap(in) char, unsigned char, signed char,
short, signed short, unsigned short,
int, signed int, unsigned int,
long, signed long, unsigned long,
float, double, long double, char *, void *, void,
enum SWIGTYPE, SWIGTYPE *,
SWIGTYPE[ANY], SWIGTYPE & "$1 = $input;";
%typemap(in) SWIGTYPE "$1 = *$input;";
</pre>
</div>
<H4><a name="Allegrocl_nn38"></a>16.4.1.2 OUT Typemap</H4>
<p>
The <tt>out</tt> typemap is used to generate code to form the
return value of the wrapper from the return value of the wrapped
function. This code is placed in the <convert and bind result to lresult>
section of the above code diagram. It's default mapping is as follows:
</p>
<div class="code">
<pre>
%typemap(out) bool "$result = (int)$1;";
%typemap(out) char, unsigned char, signed char,
short, signed short, unsigned short,
int, signed int, unsigned int,
long, signed long, unsigned long,
float, double, long double, char *, void *, void,
enum SWIGTYPE, SWIGTYPE *,
SWIGTYPE[ANY], SWIGTYPE & "$result = $1;";
%typemap(out) SWIGTYPE "$result = new $1_type($1);";
</pre>
</div>
<H4><a name="Allegrocl_nn39"></a>16.4.1.3 CTYPE Typemap</H4>
<p>
This typemap is not used for code generation, but purely for the
transformation of types in the parameter list of the wrapper function.
It's primary use is to handle by-value to by-reference conversion in the
wrappers parameter list. Its default settings are:
</p>
<div class="code">
<pre>
%typemap(ctype) bool "int";
%typemap(ctype) char, unsigned char, signed char,
short, signed short, unsigned short,
int, signed int, unsigned int,
long, signed long, unsigned long,
float, double, long double, char *, void *, void,
enum SWIGTYPE, SWIGTYPE *,
SWIGTYPE[ANY], SWIGTYPE & "$1_ltype";
%typemap(ctype) SWIGTYPE "$&1_type";
</pre>
</div>
<p>
These three typemaps are specifically employed by the the
Allegro CL interface generator. SWIG also implements a number of
other typemaps that can be used for generating code in the C/C++
wrappers. You can read about
these <a href="Typemaps.html#Typemaps_nn25">common typemaps</a> here.
</p>
<H3><a name="Allegrocl_nn40"></a>16.4.2 Code generation in Lisp wrappers</H3>
<p>
A number of custom typemaps have also been added, to facilitate
the generation of code in the lisp side of the interface. These
are described below. The basic code generation structure is
applied as a series of nested expressions, one for each
parameter, then one for manipulating the return value, and last,
the foreign function call itself.
</p>
<H4><a name="Allegrocl_nn41"></a>16.4.2.1 LIN Typemap</H4>
<p>
The LIN typemap allows for the manipulating the lisp objects
passed as arguments to the wrapping defun before passing them to
the foreign function call. For example, when passing lisp
strings to foreign code, it is often necessary to copy the
string into a foreign structure of type (:char *) of appropriate
size, and pass this copy to the foreign call. Using the LIN
typemap, one could arrange for the stack-allocation of a foreign
char array, copy your string into it, and not have to worry
about freeing the copy after the function returns.
</p>
<p>The LIN typemap accepts the following <tt>$variable</tt> references.
</p>
<ul>
<li><tt>$in</tt> - expands to the name of the parameter being
applied to this typemap
</li>
<li><tt>$out</tt> - expands to the name of the local variable
assigned to this typemap
</li>
<li><tt>$in_fftype</tt> - the foreign function type of the C type.</li>
<li><tt>$*in_fftype</tt> - the foreign function type of the C type
with one pointer removed. If there is no pointer, then $*in_fftype
is the same as $in_fftype.
</li>
<li><tt>$body</tt> - very important. Instructs SWIG where
subsequent code generation steps should be inserted into the
current typemap. Leaving out a <tt>$body</tt> reference
will result in lisp wrappers that do very little by way of
calling into foreign code. Not recommended.
</li>
</ul>
<div class="code">
<pre>
%typemap(lin) SWIGTYPE "(let (($out $in))\n $body)";
</pre>
</div>
<H4><a name="Allegrocl_nn42"></a>16.4.2.2 LOUT Typemap</H4>
<p>
The LOUT typemap is the means by which we effect the wrapping of
foreign pointers in CLOS instances. It is applied after all LIN
typemaps, and immediately before the actual foreign-call.
</p>
<p>The LOUT typemap uses the following $variable
</p>
<ul>
<li><tt>$lclass</tt> - Expands to the CLOS class that
represents foreign-objects of the return type matching this
typemap.
</li>
<li><tt>$body</tt> - Same as for the LIN map. Place this
variable where you want the foreign-function call to occur.
</li>
<li><tt>$ldestructor</tt> - Expands to the symbol naming the destructor for this
class ($lclass) of object. Allows you to insert finalization or automatic garbage
collection into the wrapper code (see default mappings below).
</li>
</ul>
<div class="code">
<pre>
%typemap(lout) bool, char, unsigned char, signed char,
short, signed short, unsigned short,
int, signed int, unsigned int,
long, signed long, unsigned long,
float, double, long double, char *, void *, void,
enum SWIGTYPE "$body";
%typemap(lout) SWIGTYPE[ANY], SWIGTYPE *,
SWIGTYPE & "(make-instance '$lclass :foreign-address $body)";
%typemap(lout) SWIGTYPE "(let* ((address $body)\n
(ACL_result (make-instance '$lclass :foreign-address address)))\n
(unless (zerop address)\n
(excl:schedule-finalization ACL_result #'$ldestructor))\n
ACL_result)";
</pre>
</div>
<H4><a name="Allegrocl_nn43"></a>16.4.2.3 FFITYPE Typemap</H4>
<p>
The FFITYPE typemap works as a helper for a body of code that
converts C/C++ type specifications into Allegro CL foreign-type
specifications. These foreign-type specifications appear in
ff:def-foreing-type declarations, and in the argument list and
return values of ff:def-foreign-calls. You would modify this
typemap if you want to change how the FFI passes through
arguments of a given type. For example, if you know that a
particular compiler represents booleans as a single byte, you
might add an entry for:
</p>
<div class="code">
<pre>
%typemap(ffitype) bool ":unsigned-char";
</pre>
</div>
<p>
Note that this typemap is pure type transformation, and is not
used in any code generations step the way the LIN and LOUT
typemaps are. The default mappings for this typemap are:
</p>
<div class="code">
<pre>
%typemap(ffitype) bool ":int";
%typemap(ffitype) char ":char";
%typemap(ffitype) unsigned char ":unsigned-char";
%typemap(ffitype) signed char ":char";
%typemap(ffitype) short, signed short ":short";
%typemap(ffitype) unsigned short ":unsigned-short";
%typemap(ffitype) int, signed int ":int";
%typemap(ffitype) unsigned int ":unsigned-int";
%typemap(ffitype) long, signed long ":long";
%typemap(ffitype) unsigned long ":unsigned-long";
%typemap(ffitype) float ":float";
%typemap(ffitype) double ":double";
%typemap(ffitype) char * "(* :char)";
%typemap(ffitype) void * "(* :void)";
%typemap(ffitype) void ":void";
%typemap(ffitype) enum SWIGTYPE ":int";
%typemap(ffitype) SWIGTYPE & "(* :void)";
</pre>
</div>
<H4><a name="Allegrocl_nn44"></a>16.4.2.4 LISPTYPE Typemap</H4>
<p>
This is another type only transformation map, and is used to
provide the lisp-type, which is the optional third argument in
argument specifier in a ff:def-foreign-call form. Specifying a
lisp-type allows the foreign call to perform type checking on
the arguments passed in. The default entries in this typemap are:
</p>
<div class="code">
<pre>
%typemap(lisptype) bool "boolean";
%typemap(lisptype) char "character";
%typemap(lisptype) unsigned char "integer";
%typemap(lisptype) signed char "integer";
</pre>
</div>
<H4><a name="Allegrocl_nn45"></a>16.4.2.5 LISPCLASS Typemap</H4>
<p>
The LISPCLASS typemap is used to generate the method signatures
for the generic-functions which wrap overloaded functions and
functions with defaulted arguments. The default entries are:
</p>
<div class="code">
<pre>
%typemap(lispclass) bool "t";
%typemap(lispclass) char "character";
%typemap(lispclass) unsigned char, signed char,
short, signed short, unsigned short,
int, signed int, unsigned int,
long, signed long, unsigned long,
enum SWIGTYPE "integer";
%typemap(lispclass) float "single-float";
%typemap(lispclass) double "double-float";
%typemap(lispclass) char * "string";
</pre>
</div>
<H3><a name="Allegrocl_nn46"></a>16.4.3 Modifying SWIG behavior using typemaps</H3>
<p>
The following example shows how we made use of the above
typemaps to add support for the wchar_t type.
</p>
<div class="code">
<pre>
%typecheck(SWIG_TYPECHECK_UNICHAR) wchar_t { $1 = 1; };
%typemap(in) wchar_t "$1 = $input;";
%typemap(lin) wchar_t "(let (($out (char-code $in)))\n $body)";
%typemap(lin) wchar_t* "(excl:with-native-string
($out $in
:external-format #+little-endian :fat-le
#-little-endian :fat)\n
$body)"
%typemap(out) wchar_t "$result = $1;";
%typemap(lout) wchar_t "(code-char $body)";
%typemap(lout) wchar_t* "(excl:native-to-string $body
:external-format #+little-endian :fat-le
#-little-endian :fat)";
%typemap(ffitype) wchar_t ":unsigned-short";
%typemap(lisptype) wchar_t "";
%typemap(ctype) wchar_t "wchar_t";
%typemap(lispclass) wchar_t "character";
%typemap(lispclass) wchar_t* "string";
</pre>
</div>
<H2><a name="Allegrocl_nn47"></a>16.5 Identifier Converter functions</H2>
<H3><a name="Allegrocl_nn48"></a>16.5.1 Creating symbols in the lisp environment</H3>
<p>
Various symbols must be generated in the lisp environment to which
class definitions, functions, constants, variables, etc. must be
bound. Rather than force a particular convention for naming these
symbols, an identifier (to symbol) conversion function is used. A
user-defined identifier-converter can then implement any symbol
naming, case-modifying, scheme desired.
</p>
<p>
In generated SWIG code, whenever some interface object must be
referenced by its lisp symbol, a macro is inserted that calls the
identifier-converter function to generate the appropriate symbol
reference. It is therefore expected that the identifier-converter
function reliably return the same (eq) symbol given the same set
of arguments.
</p>
<H3><a name="Allegrocl_nn49"></a>16.5.2 Existing identifier-converter functions</H3>
<p>Two basic identifier routines have been defined.
<H4><a name="Allegrocl_nn50"></a>16.5.2.1 identifier-convert-null</H4>
<p>
No modification of the identifier string is performed. Based on
other arguments, the identifier may be concatenated with other
strings, from which a symbol will be created.
</p>
<H4><a name="Allegrocl_nn51"></a>16.5.2.2 identifier-convert-lispify</H4>
<p>
All underscores in the identifier string are converted to
hyphens. Otherwise, identifier-convert-lispify performs the
same symbol transformations.
</p>
<H4><a name="Allegrocl_nn52"></a>16.5.2.3 Default identifier to symbol conversions</H4>
<p>
Check the definitions of the above two default
identifier-converters in <tt>Lib/allegrocl/allegrocl.swg</tt> for
default naming conventions.
</p>
<H3><a name="Allegrocl_nn53"></a>16.5.3 Defining your own identifier-converter</H3>
<p>
A user-defined identifier-converter function should conform to the following
specification:
</p>
<div class="targetlang">
<pre>
(defun identifier-convert-fn (id &key type class arity) ...body...)
result ==> symbol or (setf symbol)
</pre>
</div>
<p>The <tt>ID</tt> argument is a string representing an identifier in the
foreign environment.
</p>
<p>
The :type keyword argument provides more information on the type of
identifier. It's value is a symbol. This allows the
identifier-converter to apply different heuristics when mapping
different types of identifiers to symbols. SWIG will generate calls
to your identifier-converter using the following types.
</p>
<ul>
<li>:class - names a CLOS class.</li>
<li>:constant - names a defconstant</li>
<li>:constructor - names a function for creating a foreign object</li>
<li>:destructor - names a function for freeing a foreign object</li>
<li>:function - names a CLOS wrapping defmethod or defun.</li>
<li>:ff-operator - names a foreign call defined via ff:def-foreign-call</li>
<li>:getter - getter function</li>
<li>:namespace - names a C++ namespace</li>
<li>:setter - names a setter function. May return a (setf symbol) reference</li>
<li>:operator - names a C++ operator, such as Operator=, Operator*.</li>
<li>:slot - names a slot in a struct/class/union declaration.</li>
<li>:type - names a foreign-type defined via ff:def-foreign-type.</li>
<li>:variable - names a variable defined via ff:def-foreign-variable.</li>
</ul>
<p>
The :class keyword argument is a string naming a foreign
class. When non-nil, it indicates that the current identifier has
scope in the specified class.
</p>
<p>
The :arity keyword argument only appears in swig:swig-defmethod forms
generated for overloaded functions. It's value is an integer
indicating the number of arguments passed to the routine indicated by
this identifier.
</p>
<H3><a name="Allegrocl_nn54"></a>16.5.4 Instructing SWIG to use a particular identifier-converter</H3>
<p>
By default, SWIG will use identifier-converter-null. To specify
another convert function, use the <tt>-identifier-converter</tt>
command-line argument. The value should be a string naming the
function you wish the interface to use instead, when generating
symbols. ex:
</p>
<div class="code">
<pre>
% swig -allegrocl -c++ -module mymodule -identifier-converter my-identifier-converter
</pre>
</div>
</body>
</html>