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<H1><a name="Guile"></a>19 SWIG and Guile</H1>
<!-- INDEX -->
<div class="sectiontoc">
<ul>
<li><a href="#Guile_nn2">Meaning of "Module"</a>
<li><a href="#Guile_nn3">Using the SCM or GH Guile API</a>
<li><a href="#Guile_nn4">Linkage</a>
<ul>
<li><a href="#Guile_nn5">Simple Linkage</a>
<li><a href="#Guile_nn6">Passive Linkage</a>
<li><a href="#Guile_nn7">Native Guile Module Linkage</a>
<li><a href="#Guile_nn8">Old Auto-Loading Guile Module Linkage</a>
<li><a href="#Guile_nn9">Hobbit4D Linkage</a>
</ul>
<li><a href="#Guile_nn10">Underscore Folding</a>
<li><a href="#Guile_nn11">Typemaps</a>
<li><a href="#Guile_nn12">Representation of pointers as smobs</a>
<ul>
<li><a href="#Guile_nn13">GH Smobs</a>
<li><a href="#Guile_nn14">SCM Smobs</a>
<li><a href="#Guile_nn15">Garbage Collection</a>
</ul>
<li><a href="#Guile_nn16">Exception Handling</a>
<li><a href="#Guile_nn17">Procedure documentation</a>
<li><a href="#Guile_nn18">Procedures with setters</a>
<li><a href="#Guile_nn19">GOOPS Proxy Classes</a>
<ul>
<li><a href="#Guile_nn20">Naming Issues</a>
<li><a href="#Guile_nn21">Linking</a>
</ul>
</ul>
</div>
<!-- INDEX -->



<p>
This section details guile-specific support in SWIG.

<H2><a name="Guile_nn2"></a>19.1 Meaning of "Module"</H2>


<p>
There are three different concepts of "module" involved, defined
separately for SWIG, Guile, and Libtool.  To avoid horrible confusion,
we explicitly prefix the context, e.g., "guile-module".

<H2><a name="Guile_nn3"></a>19.2 Using the SCM or GH Guile API</H2>


<p>The guile module can currently export wrapper files that use the guile GH interface or the
SCM interface. This is controlled by an argument passed to swig.  The "-gh" argument causes swig
to output GH code, and the "-scm" argument causes swig to output SCM code.  Right now the "-scm" argument
is the default.  The "-scm" wrapper generation assumes a guile version &gt;= 1.6 and has several advantages over
the "-gh" wrapper generation including garbage collection and GOOPS support.
The "-gh" wrapper generation can be used for older versions of guile.
The guile GH wrapper code generation is depreciated and the
SCM interface is the default.  The SCM and GH interface differ greatly in how they store
pointers and have completely different run-time code. See below for more info.  

<p>The GH interface to guile is deprecated.  Read more about why in the 
<a href="http://www.gnu.org/software/guile/docs/guile-ref/GH-deprecation.html">Guile manual</a>.
The idea of the GH interface was to provide a high level API that other languages and projects
could adopt.  This was a good idea, but didn't pan out well for general development.  But for the
specific, minimal uses that the SWIG typemaps put the GH interface to use is ideal for
using a high level API.  So even though the GH interface is depreciated, SWIG will continue to use
the GH interface and provide mappings from the GH interface to whatever API we need.
We can maintain this mapping where guile failed because SWIG uses a small subset of all the GH functions 
which map easily.  All the guile typemaps like typemaps.i and std_vector.i
will continue to use the GH functions to do things like create lists of values, convert strings to
integers, etc.  Then every language module will define a mapping between the GH interface and 
whatever custom API the language uses.  This is currently implemented by the guile module to use
the SCM guile API rather than the GH guile API.  
For example, here are some of the current mapping file for the SCM API</p>

<div class="code"><pre>

#define gh_append2(a, b) scm_append(scm_listify(a, b, SCM_UNDEFINED)) 
#define gh_apply(a, b) scm_apply(a, b, SCM_EOL) 
#define gh_bool2scm SCM_BOOL 
#define gh_boolean_p SCM_BOOLP 
#define gh_car SCM_CAR 
#define gh_cdr SCM_CDR 
#define gh_cons scm_cons 
#define gh_double2scm scm_make_real 
...
</pre></div>

<p>This file is parsed by SWIG at wrapper generation time, so every reference to a gh_ function is replaced
by a scm_ function in the wrapper file.  Thus the gh_ function calls will never be seen in the wrapper;
the wrapper will look exactly like it was generated
for the specific API.  Currently only the guile language module has created a mapping policy from gh_ to scm_,
but there is no reason other languages (like mzscheme or chicken) couldn't also use this.  
If that happens, there is A LOT less code duplication in the standard typemaps.</p>

<H2><a name="Guile_nn4"></a>19.3 Linkage</H2>


<p>
Guile support is complicated by a lack of user community cohesiveness,
which manifests in multiple shared-library usage conventions.  A set of
policies implementing a usage convention is called a <b>linkage</b>.

<H3><a name="Guile_nn5"></a>19.3.1 Simple Linkage</H3>


<p>
The default linkage is the simplest; nothing special is done.  In this
case the function <code>SWIG_init()</code> is exported. Simple linkage
can be used in several ways:
</p>

<ul>
<li><b>Embedded Guile, no modules.</b> You want to embed a Guile
interpreter into your program; all bindings made by SWIG shall show up
in the root module. Then call <code>SWIG_init()</code> in the
<code>inner_main()</code> function.  See the "simple" and "matrix" examples under
<code>Examples/guile</code>.

<li><p><b>Dynamic module mix-in.</b> You want to create a Guile module
using <code>define-module</code>, containing both Scheme code and
bindings made by SWIG; you want to load the SWIG modules as shared
libraries into Guile.</p>
<div class="targetlang">
<pre>
(define-module (my module))
(define my-so (dynamic-link "./example.so"))
(dynamic-call "SWIG_init" my-so) ; make SWIG bindings
;; Scheme definitions can go here
</pre>
</div>

<p>
Newer Guile versions provide a shorthand for <code>dynamic-link</code>
and <code>dynamic-call</code>:
</p>

<div class="targetlang">
<pre>
(load-extension "./example.so" "SWIG_init")
</pre>
</div>

<p>
You need to explicitly export those bindings made by SWIG that you
want to import into other modules:
</p>

<div class="targetlang">
<pre>
(export foo bar)
</pre>
</div>

<p>
In this example, the procedures <code>foo</code> and <code>bar</code>
would be exported.  Alternatively, you can export all bindings with the
following module-system hack:
</p>

<div class="targetlang">
<pre>
(module-map (lambda (sym var)
	      (module-export! (current-module) (list sym)))
	    (current-module))
</pre>
</div>

<p>SWIG can also generate this Scheme stub (from
<code>define-module</code> up to <code>export</code>)
semi-automagically if you pass it the command-line argument
<code>-scmstub</code>.  The code will be exported in a file called
<code><i>module</i>.scm</code> in the directory specified by <code>-outdir</code>
or the current directory if <code>-outdir</code> is not specified.  
Since SWIG doesn't know how
to load your extension module (with <code>dynamic-link</code> or
<code>load-extension</code>), you need to supply this
information by including a directive like this in the interface file:
</p>

<div class="code">
<pre>
%scheme %{ (load-extension "./example.so" "SWIG_init") %}
</pre>
</div>

<p>
(The <code>%scheme</code> directive allows to insert arbitrary Scheme
code into the generated file <code><var>module.scm</var></code>; it is
placed between the <code>define-module</code> form and the
<code>export</code> form.)
</p>
</ul>

<p>If you want to include several SWIG modules, you would need to rename
<code>SWIG_init</code> via a preprocessor define to avoid symbol
clashes. For this case, however, passive linkage is available.

<H3><a name="Guile_nn6"></a>19.3.2 Passive Linkage</H3>


<p>Passive linkage is just like simple linkage, but it generates an
initialization function whose name is derived from the module and
package name (see below). 

<p>You should use passive linkage rather than simple linkage when you
are using multiple modules.

<H3><a name="Guile_nn7"></a>19.3.3 Native Guile Module Linkage</H3>


<p>SWIG can also generate wrapper code that does all the Guile module
declarations on its own if you pass it the <code>-Linkage
module</code> command-line option. This requires Guile 1.5.0 or later.

<p>The module name is set with the <code>-package</code> and
<code>-module</code> command-line options. Suppose you want to define
a module with name <code>(my lib foo)</code>; then you would have to
pass the options <code>-package <var>my</var>/<var>lib</var> -module
<var>foo</var></code>. Note that the last part of the name can also be set
via the SWIG directive <code>%module</code>. 

<p>You can use this linkage in several ways:

<ul>
<li><b>Embedded Guile with SWIG modules.</b> You want to embed a Guile
interpreter into your program; the SWIG bindings shall be put into
different modules. Simply call the function 
<code>scm_init_<var>my</var>_<var>modules</var>_<var>foo</var>_module</code>
in the <code>inner_main()</code> function.

<li><b>Dynamic Guile modules.</b> You want to load the SWIG modules as
shared libraries into Guile; all bindings are automatically put in
newly created Guile modules. 
<div class="targetlang">
<pre>
(define my-so (dynamic-link "./foo.so"))
;; create new module and put bindings there:
(dynamic-call "scm_init_my_modules_foo_module" my-so) 
</pre>
</div>
Newer Guile versions have a shorthand procedure for this:
<div class="targetlang">
<pre>
(load-extension "./foo.so" "scm_init_my_modules_foo_module")
</pre>
</div>
</ul>

<H3><a name="Guile_nn8"></a>19.3.4 Old Auto-Loading Guile Module Linkage</H3>


<p>Guile used to support an autoloading facility for object-code
modules. This support has been marked deprecated in version 1.4.1 and
is going to disappear sooner or later. SWIG still supports building
auto-loading modules if you pass it the <code>-Linkage ltdlmod</code>
command-line option.

<p>Auto-loading worked like this: Suppose a module with name <code>(my
lib foo)</code> is required and not loaded yet.  Guile will then search
all directories in its search path
for a Scheme file <code>my/modules/foo.scm</code> or a shared library
<code><var>my</var>/<var>modules</var>/lib<var>foo</var>.so</code> (or
<code><var>my</var>/<var>modules</var>/lib<var>foo</var>.la</code>; 
see the GNU libtool documentation). If a
shared library is found that contains the symbol
<code>scm_init_<var>my</var>_<var>modules</var>_<var>foo</var>_module</code>, 
the library is loaded, and the function at that symbol is called with
no arguments in order to initialize the module.

<p>When invoked with the <code>-Linkage ltdlmod</code> command-line
option, SWIG generates an exported module initialization function with
an appropriate name. 


<H3><a name="Guile_nn9"></a>19.3.5 Hobbit4D Linkage</H3>


<p>
The only other linkage supported at this time creates shared object
libraries suitable for use by hobbit's <code>(hobbit4d link)</code>
guile module.  This is called the "hobbit" linkage, and requires also
using the "-package" command line option to set the part of the module
name before the last symbol.  For example, both command lines:
</p>

<div class="shell">
<pre>
swig -guile -package my/lib foo.i
swig -guile -package my/lib -module foo foo.i
</pre>
</div>

<p>
would create module <code>(my lib foo)</code> (assuming in the first
case foo.i declares the module to be "foo").  The installed files are
my/lib/libfoo.so.X.Y.Z and friends.  This scheme is still very
experimental; the (hobbit4d link) conventions are not well understood.
</p>

<H2><a name="Guile_nn10"></a>19.4 Underscore Folding</H2>


<p>
Underscores are converted to dashes in identifiers.  Guile support may
grow an option to inhibit this folding in the future, but no one has
complained so far.

<p>You can use the SWIG directives <code>%name</code> and
<code>%rename</code> to specify the Guile name of the wrapped
functions and variables (see CHANGES).

<H2><a name="Guile_nn11"></a>19.5 Typemaps</H2>


<p>
The Guile module handles all types via typemaps. This
information is read from <code>Lib/guile/typemaps.i</code>. 

Some non-standard typemap substitutions are supported:
<ul>
<li><code>$descriptor</code> expands to a type descriptor for use with
the <code>SWIG_NewPointerObj()</code> and
<code>SWIG_ConvertPtr</code> functions.
<li>For pointer types, <code>$*descriptor</code> expands to a
descriptor for the direct base type (i.e., one pointer is stripped),
whereas <code>$basedescriptor</code> expands to a
descriptor for the base type (i.e., all pointers are stripped).
</ul>

<p>A function returning <code>void</code> (more precisely, a function
whose <code>out</code> typemap returns <code>SCM_UNSPECIFIED</code>) is
treated as returning no values. In <code>argout</code> typemaps, one
can use the macro <code>GUILE_APPEND_RESULT</code> in order to append
a value to the list of function return values.

<p>Multiple values can be passed up to Scheme in one of three ways:
<ul>
<li><p><em>Multiple values as lists.</em> 
By default, if more than one value is to
be returned, a list of the values is created and returned; to switch
back to this behavior, use</p>

<div class="code">
<pre>
%values_as_list;</pre>
</div>

<li><p><em>Multiple values as vectors.</em>
By issuing 
</p>

<div class="code">
<pre>
%values_as_vector;</pre>
</div>

<p>
vectors instead of lists will be used.
<li><p><em>Multiple values for multiple-value continuations.</em>
<strong>This is the most elegant way.</strong> By issuing 
</p>

<div class="code">
<pre>
%multiple_values;</pre>
</div>

<p>
multiple values are passed to the multiple-value
continuation, as created by <code>call-with-values</code> or the
convenience macro <code>receive</code>. The latter is available if you
issue <code>(use-modules (srfi srfi-8))</code>. Assuming that your
<code>divide</code> function 
wants to return two values, a quotient and a remainder, you can write: 
</p>

<div class="targetlang">
<pre>
(receive (quotient remainder)
    (divide 35 17)
  <var>body</var>...)
</pre>
</div>

<p>
In <code><var>body</var></code>, the first result of
<code>divide</code> will be bound to the variable
<code>quotient</code>, and the second result to <code>remainder</code>.
</p>

</ul>

<p>
See also the "multivalue" example.
</p>

<p>Constants are exported as a function that returns the value.  The
%feature("constasvar") can be applied to any constant, immutable variable, or enum.
Instead of exporting the constant as a function that must be called, the
constant will appear as a scheme variable. See
<a href="Customization.html#features">Features and the %feature directive</a>
for info on how to apply the %feature.</p>

<H2><a name="Guile_nn12"></a>19.6 Representation of pointers as smobs</H2>


<p>
For pointer types, SWIG uses Guile smobs. SWIG smobs print
like this: <code>#&lt;swig struct xyzzy * 0x1234affe&gt;</code>  Two of
them are <code>equal?</code> if and only if they have the same type
and value.

<p>
To construct a Scheme object from a C pointer, the wrapper code calls
the function <code>SWIG_NewPointerObj()</code>, passing a pointer to a
struct representing the pointer type. The type index to store in the
upper half of the CAR is read from this struct.
To get the pointer represented by a smob, the wrapper code calls the
function <code>SWIG_ConvertPtr()</code>, passing a pointer to a struct
representing the expected pointer type.  See also 
<a href="Typemaps.html#runtime_type_checker">The run-time type checker</a>.
If the Scheme object passed was not a SWIG smob representing a compatible
pointer, a <code>wrong-type-arg</code> exception is raised.

<H3><a name="Guile_nn13"></a>19.6.1 GH Smobs</H3>


<p>
In earlier versions of SWIG, C pointers were represented as Scheme
strings containing a hexadecimal rendering of the pointer value and a
mangled type name.  As Guile allows registering user types, so-called
"smobs" (small objects), a much cleaner representation has been
implemented now.  The details will be discussed in the following.
</p>

<p> A smob is a cons cell where the lower half of the CAR contains the smob type
tag, while the upper half of the CAR and the whole CDR are available. Every
module creates its own smob type in the clientdata field of the module. So the
lower 16 bits of the car of the smob store the tag and the upper 16 bits store
the index this type is in the array. We can then, given a smob, find its
swig_type_info struct by using the tag (lower 16 bits of car) to find which
module this type is in (since each tag is unique for the module). Then we use
the upper 16 bits to index into the array of types attached to this module.
Looking up the module from the tag is worst case O(# of modules) but average
case O(1). This is because the modules are stored in a circularly linked list,
and when we start searching the modules for the tag, we start looking with the
module that the function doing the lookup is in. SWIG_Guile_ConvertPtr() takes
as its first argument the swig_module_info * of the calling function, which is
where we start comparing tags. Most types will be looked up in the same module
that created them, so the first module we check will most likely be correct.
Once we have a swig_type_info structure, we loop through the linked list of
casts, using pointer comparisons.</p>

<H3><a name="Guile_nn14"></a>19.6.2 SCM Smobs</H3>


<p>The SCM interface (using the "-scm" argument to swig) uses swigrun.swg.
The whole type system, when it is first initialized, creates two smobs named "swig" and "collected_swig".
The swig smob is used for non-garbage collected smobs, while the collected_swig smob is used as described
below.  Each smob has the same format, which is a double cell created by SCM_NEWSMOB2()
The first word of data is the pointer to the object and the second word of data is the swig_type_info *
structure describing this type.  This is a lot easier than the GH interface above because we can store
a pointer to the type info structure right in the type.  With the GH interface, there was not enough
room in the smob to store two whole words of data so we needed to store part of the "swig_type_info address"
in the smob tag.  If a generated GOOPS module has been loaded, smobs will be wrapped by the corresponding
GOOPS class.</p>


<H3><a name="Guile_nn15"></a>19.6.3 Garbage Collection</H3>


<p>Garbage collection is a feature of the new SCM interface, and it is automatically included
if you pass the "-scm" flag to swig.  Thus the swig garbage collection support requires guile &gt;1.6.
Garbage collection works like this.  Every swig_type_info structure stores in its clientdata field a pointer
to the destructor for this type.  The destructor is the generated wrapper around the delete function.
So swig still exports a wrapper for the destructor, it just does not call scm_c_define_gsubr() for
the wrapped delete function.  So the only way to delete an object is from the garbage collector, since the
delete function is not available to scripts.  How swig determines if a type should be garbage collected
is exactly like described in <a href="Customization.html#ownership">
Object ownership and %newobject</a> in the SWIG manual.  All typemaps use an $owner var, and
the guile module replaces $owner with 0 or 1 depending on feature:new.</p>

<H2><a name="Guile_nn16"></a>19.7 Exception Handling</H2>


<p>
SWIG code calls <code>scm_error</code> on exception, using the following
mapping:

<div class="code">
<pre>
      MAP(SWIG_MemoryError,	"swig-memory-error");
      MAP(SWIG_IOError,		"swig-io-error");
      MAP(SWIG_RuntimeError,	"swig-runtime-error");
      MAP(SWIG_IndexError,	"swig-index-error");
      MAP(SWIG_TypeError,	"swig-type-error");
      MAP(SWIG_DivisionByZero,	"swig-division-by-zero");
      MAP(SWIG_OverflowError,	"swig-overflow-error");
      MAP(SWIG_SyntaxError,	"swig-syntax-error");
      MAP(SWIG_ValueError,	"swig-value-error");
      MAP(SWIG_SystemError,	"swig-system-error");
</pre>
</div>

<p>
The default when not specified here is to use "swig-error".
See Lib/exception.i for details.

<H2><a name="Guile_nn17"></a>19.8 Procedure documentation</H2>


<p>If invoked with the command-line option <code>-procdoc
<var>file</var></code>, SWIG creates documentation strings for the
generated wrapper functions, describing the procedure signature and
return value, and writes them to <var>file</var>. You need Guile 1.4
or later to make use of the documentation files.

<p>SWIG can generate documentation strings in three formats, which are
selected via the command-line option <code>-procdocformat
<var>format</var></code>:
<ul>
<li><code>guile-1.4</code> (default): Generates a format suitable for Guile 1.4.
<li><code>plain</code>: Generates a format suitable for Guile 1.4.1 and
later.
<li><code>texinfo</code>: Generates texinfo source, which must be run
through texinfo in order to get a format suitable for Guile 1.4.1 and
later.
</ul>

<p>You need to register the generated documentation file with Guile
like this:

<div class="targetlang">
<pre>
(use-modules (ice-9 documentation))
(set! documentation-files 
      (cons "<var>file</var>" documentation-files))
</pre>
</div>

<p>Documentation strings can be configured using the Guile-specific
typemap argument <code>doc</code>. See <code>Lib/guile/typemaps.i</code> for
details.

<H2><a name="Guile_nn18"></a>19.9 Procedures with setters</H2>


<p>For global variables, SWIG creates a single wrapper procedure
<code>(<var>variable</var> :optional value)</code>, which is used for
both getting and setting the value. For struct members, SWIG creates
two wrapper procedures <code>(<var>struct</var>-<var>member</var>-get
pointer)</code> and <code>(<var>struct-member</var>-set pointer value)</code>.

<p>If invoked with the command-line option <code>-emit-setters</code>
(<em>recommended</em>),
SWIG will additionally create procedures with setters. For global
variables, the procedure-with-setter <code><var>variable</var></code>
is created, so you can use <code>(<var>variable</var>)</code> to get
the value and <code>(set! (<var>variable</var>)
<var>value</var>)</code> to set it. For struct members, the
procedure-with-setter <code><var>struct</var>-<var>member</var></code>
is created, so you can use <code>(<var>struct</var>-<var>member</var>
<var>pointer</var>)</code> to get the value and <code>(set!
(<var>struct</var>-<var>member</var> <var>pointer</var>)
<var>value</var>)</code> to set it.

<p>If invoked with the command-line option <code>-only-setters</code>,
SWIG will <em>only</em> create procedures with setters, i.e., for
struct members, the procedures <code>(<var>struct</var>-<var>member</var>-get
pointer)</code> and <code>(<var>struct-member</var>-set pointer
value)</code> are <em>not</em> generated.

<H2><a name="Guile_nn19"></a>19.10 GOOPS Proxy Classes</H2>


<p>SWIG can also generate classes and generic functions for use with
Guile's Object-Oriented Programming System (GOOPS).  GOOPS is a
sophisticated object system in the spirit of the Common Lisp Object
System (CLOS).

<p>GOOPS support is
only available with the new SCM interface (enabled with the
<code>-scm</code> command-line option of SWIG).  To enable GOOPS
support, pass the <code>-proxy</code> argument to
swig.  This will export the GOOPS wrapper definitions into the
<code><i>module</i>.scm</code> file in the directory specified by -outdir or the
current directory.  GOOPS support requires either passive or module linkage.</p>

<p>The generated file will contain definitions of GOOPS classes mimicking the C++ class hierarchy.
<p>Enabling GOOPS support implies <code>-emit-setters</code>.

<p>If <code>-emit-slot-accessors</code> is also passed as an argument,
then the generated file will contain accessor methods for all the
slots in the classes and for global variables.  The input class</p>
<div class="code"><pre>
  class Foo {
    public:
      Foo(int i) : a(i) {}
      int a;
      int getMultBy(int i) { return a * i; }
      Foo getFooMultBy(int i) { return Foo(a * i); }
  }; 
  Foo getFooPlus(int i) { return Foo(a + i); }
</pre></div>

<p>
will produce (if <code>-emit-slot-accessors</code> is not passed as a parameter)
</p>

<div class="targetlang"><pre>
(define-class &lt;Foo&gt; (&lt;swig&gt;)
  (a #:allocation #:swig-virtual 
     #:slot-ref primitive:Foo-a-get 
     #:slot-set! primitive:Foo-a-set)
  #:metaclass &lt;swig-metaclass&gt;
  #:new-function primitive:new-Foo
)
(define-method (getMultBy (swig_smob &lt;Foo&gt;) i)
  (primitive:Foo-getMultBy  (slot-ref swig_smob 'smob) i))
(define-method (getFooMultBy (swig_smob &lt;Foo&gt;) i)
  (make &lt;Foo&gt; #:init-smob (primitive:Foo-getFooMultBy  (slot-ref swig_smob 'smob) i)))

(define-method (getFooPlus i)
  (make &lt;Foo&gt; #:init-smob (primitive:getFooPlus i)))

(export &lt;Foo&gt; getMultBy getFooMultBy getFooPlus )
</pre></div>

<p>
and will produce (if <code>-emit-slot-accessors</code> is passed as a parameter)
</p>

<div class="targetlang"><pre>
(define-class &lt;Foo&gt; (&lt;swig&gt;)
  (a #:allocation #:swig-virtual 
     #:slot-ref primitive:Foo-a-get 
     #:slot-set! primitive:Foo-a-set 
     <b>#:accessor a</b>)
  #:metaclass &lt;swig-metaclass&gt;
  #:new-function primitive:new-Foo
)
(define-method (getMultBy (swig_smob &lt;Foo&gt;) i)
  (primitive:Foo-getMultBy  (slot-ref swig_smob 'smob) i))
(define-method (getFooMultBy (swig_smob &lt;Foo&gt;) i)
  (make &lt;Foo&gt; #:init-smob (primitive:Foo-getFooMultBy  (slot-ref swig_smob 'smob) i)))

(define-method (getFooPlus i)
  (make &lt;Foo&gt; #:init-smob (primitive:getFooPlus i)))

(export &lt;Foo&gt; <b>a</b> getMultBy getFooMultBy getFooPlus )
</pre></div>

<p>
which can then be used by this code
</p>

<div class="targetlang"><pre>
;; not using getters and setters
(define foo (make &lt;Foo&gt; #:args '(45)))
(slot-ref foo 'a)
(slot-set! foo 'a 3)
(getMultBy foo 4)
(define foo2 (getFooMultBy foo 7))
(slot-ref foo 'a)
(slot-ref (getFooPlus foo 4) 'a)

;; using getters and setters
(define foo (make &lt;Foo&gt; #:args '(45)))
(a foo)
(set! (a foo) 5)
(getMultBy foo 4)
(a (getFooMultBy foo 7))
</pre></div>

<p>Notice that constructor arguments are passed as a list after the <code>#:args</code> keyword.  Hopefully in
the future the following will be valid <code>(make &lt;Foo&gt; #:a 5 #:b 4)</code></p>

<p>Also note that the order the declarations occur in the .i file make a difference.  For example,
</p>

<div class="code"><pre>
%module test

%{ #include "foo.h" %}

%inline %{
  int someFunc(Foo &amp;a) {
    ...
  }
%}

%include "foo.h"
</pre></div>

<p>
This is a valid SWIG file it will work as you think it will for primitive support, but the generated
GOOPS file will be broken.  Since the <code>someFunc</code> definition is parsed by SWIG before all the
declarations in foo.h, the generated GOOPS file will contain the definition of <code>someFunc()</code>
before the definition of &lt;Foo&gt;.  The generated GOOPS file would look like
</p>

<div class="targetlang"><pre>
;;...

(define-method (someFunc (swig_smob &lt;Foo&gt;))
  (primitive:someFunc (slot-ref swig_smob 'smob)))

;;...

(define-class &lt;Foo&gt; (&lt;swig&gt;)
  ;;...
)

;;...
</pre></div>

<p>
Notice that &lt;Foo&gt; is used before it is defined.  The fix is to just put the 
<code>%import "foo.h"</code> before the <code>%inline</code> block.
</p>

<H3><a name="Guile_nn20"></a>19.10.1 Naming Issues</H3>


<p>As you can see in the example above, there are potential naming conflicts.  The default exported
accessor for the <code>Foo::a</code> variable is named <code>a</code>.  The name of the wrapper global 
function is <code>getFooPlus</code>.
If the <code>-useclassprefix</code> option is passed to swig, the name of all accessors and member 
functions will be prepended with the class name.  So the accessor will be called <code>Foo-a</code> and 
the member functions will be called <code>Foo-getMultBy</code>.  Also, if the 
<code>-goopsprefix goops:</code> argument is passed to swig, every identifier will be prefixed by 
<code>goops:</code></p>

<p>Two guile-modules are created by SWIG.  The first module contains the primitive definitions
of all the wrapped functions and variables, and is located either in the _wrap.cxx file (with <code>-Linkage
module</code>) or in the scmstub file (if <code>-Linkage passive -scmstub</code>).  The name of this 
guile-module is the swig-module name (given on the command line with the -module argument or with the 
%module directive) concatenated with the string "-primitive".  For
example, if <code>%module Test</code> is set in the swig interface file, the name of the guile-module in 
the scmstub or <code>-Linkage module</code> will be <code>Test-primitive</code>.  Also, the scmstub
file will be named <code>Test-primitive.scm</code>.
The string "primitive" can be changed by the <code>-primsuffix</code> swig
argument.  So the same interface, with the <code>-primsuffix base</code> will produce a module called 
<code>Test-base</code>. 
The second generated guile-module contains all the GOOPS class definitions and is located in
a file named <i>module</i>.scm in the directory specified with -outdir or the current directory.
The name of this guile-module is the name of the
swig-module (given on the command line or with the <code>%module</code> directive).
In the previous example, the GOOPS definitions will be in a file named Test.scm.</p>

<p>Because of the naming conflicts, you can't in general use both the <code>-primitive</code> and the GOOPS 
guile-modules at the same time.  To do this, you need to rename the exported symbols from one or both 
guile-modules.  For example,</p>
<div class="targetlang"><pre>
(use-modules ((Test-primitive) #:renamer (symbol-prefix-proc 'primitive:)))
(use-modules ((Test) #:renamer (symbol-prefix-proc 'goops:)))
</pre></div>

<p>TODO: Renaming class name prefixes?</p>

<H3><a name="Guile_nn21"></a>19.10.2 Linking</H3>


<p>The guile-modules generated above all need to be linked together.  GOOPS support requires
either passive or module linkage.  The exported GOOPS guile-module will be the name of the swig-module
and should be located in a file called <i>Module</i>.scm.  This should be installed on the autoload
path for guile, so that <code>(use-modules (<i>Package Module</i>))</code> will load everything needed.
Thus, the top of the GOOPS guile-module will contain code to load everything needed by the interface 
(the shared library, the scmstub module, etc.).
The <code>%goops</code> directive inserts arbitrary code into the generated GOOPS guile-module, and
should be used to load the dependent libraries.</p>

<p>This breaks up into three cases</p>
<ul>
<li><b>Passive Linkage without -scmstub</b>:  Note that this linkage style has the potential for naming
conflicts, since the primitive exported function and variable names are not wrapped in a guile-module
and might conflict with names from the GOOPS guile-module (see above).  Pass the -goopsprefix
argument to solve this problem.  If the <code>-exportprimitive</code> option is passed to SWIG the
<code>(export ...)</code> code that would be exported into the scmstub file is exported at the bottom 
of the generated GOOPS guile-module.
The <code>%goops</code> directive should contain code to load the .so library.

<div class="code"><pre>
%goops %{ (load-extension "./foo.so" "scm_init_my_modules_foo_module") %}
</pre></div>

<p>
Produces the following code at the top of the generated GOOPS guile-module 
(with the <code>-package my/modules -module foo</code> command line arguments)
</p>

<div class="targetlang"><pre>
(define-module (my modules foo))

;; %goops directive goes here
(load-extension "./foo.so" "scm_init_my_modules_foo_module") 

(use-modules (oop goops) (Swig common))
</pre></div>
</li>

<li><p><b>Passive Linkage with -scmstub</b>: Here, the name of the scmstub file should be
<code>Module-primitive.scm</code> (with <i>primitive</i> replaced with whatever is given with the <code>-primsuffix</code>
argument.  The code to load the <code>.so</code> library should be located in the <code>%scheme</code> directive, 
which will then be added to the scmstub file.
Swig will automatically generate the line <code>(use-modules (<i>Package</i> <i>Module-primitive</i>))</code>
into the GOOPS guile-module.  So if <i>Module-primitive.scm</i> is on the autoload path for guile, the
<code>%goops</code> directive can be empty.  Otherwise, the <code>%goops</code> directive should contain 
whatever code is needed to load the <i>Module-primitive.scm</i> file into guile.</p>

<div class="targetlang"><pre>
%scheme %{ (load-extension "./foo.so" "scm_init_my_modules_foo_module") %}
// only include the following definition if (my modules foo) cannot
// be loaded automatically
%goops %{ 
  (primitive-load "/path/to/foo-primitive.scm") 
  (primitive-load "/path/to/Swig/common.scm")
%}
</pre></div>

<p>
Produces the following code at the top of the generated GOOPS guile-module
</p>

<div class="targetlang"><pre>
(define-module (my modules foo))

;; %goops directive goes here (if any)
(primitive-load "/path/to/foo-primitive.scm")
(primitive-load "/path/to/Swig/common.scm")

(use-modules (oop goops) (Swig common))
(use-modules ((my modules foo-primitive) :renamer (symbol-prefix-proc
                                                       'primitive:)))

</pre></div>
</li>

<li><p><b>Module Linkage</b>: This is very similar to passive linkage with a scmstub file.
Swig will also automatically generate the line <code>(use-modules 
(<i>Package</i> <i>Module-primitive</i>))</code> into the GOOPS guile-module.  Again the <code>%goops</code>
directive should contain whatever code is needed to get that module loaded into guile.</p>

<div class="code"><pre>
%goops %{ (load-extension "./foo.so" "scm_init_my_modules_foo_module") %}
</pre></div>

<p>
Produces the following code at the top of the generated GOOPS guile-module
</p>

<div class="targetlang"><pre>
(define-module (my modules foo))

;; %goops directive goes here (if any)
(load-extension "./foo.so" "scm_init_my_modules_foo_module") 

(use-modules (oop goops) (Swig common))
(use-modules ((my modules foo-primitive) :renamer (symbol-prefix-proc
                                                         'primitive:)))

</pre></div>
</li>
</ul>

<p><b>(Swig common)</b>: The generated GOOPS guile-module also imports definitions from the 
(Swig common) guile-module.
This module is included with SWIG and should be installed by SWIG into the autoload path for
guile (based on the configure script and whatever arguments are passed).  If it is not, then the
<code>%goops</code> directive also needs to contain code to load the <code>common.scm</code> file
into guile.  Also note that if you are trying to install the generated wrappers on a computer without
SWIG installed, you will need to include the common.swg file along with the install.</p>

<p><b>Multiple Modules</b>:  Type dependencies between modules is supported.  For example, if
<code>mod1</code> includes definitions of some classes, and <code>mod2</code> includes some classes
derived from classes in <code>mod1</code>, the generated GOOPS file for <code>mod2</code> will declare
the correct superclasses.  The only problem is that since <code>mod2</code> uses symbols from
<code>mod1</code>, the <code>mod2</code> GOOPS file must include a <code>(use-modules (mod2))</code>.
Currently, SWIG does not automatically export this line;  it must be included in the <code>%goops</code>
directive of <code>mod2</code>.  Maybe in the future SWIG can detect dependencies and export this line.
(how do other language modules handle this problem?)</p>

</body>
</html>
Summary ✨

This HTML code documents how to use SWIG (Simplified Wrapper and Interface Generator) to generate wrappers for C/C++ code in a programming language like Python, Ruby, etc. It explains three types of linkage: passive linkage with a SCM file, module linkage, and how to handle type dependencies between modules.
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