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<title>Foreign Objects (Guile Reference Manual)</title>
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<div class="section-level-extent" id="Foreign-Objects">
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Next: <a href="Smobs.html" accesskey="n" rel="next">Smobs</a>, Previous: <a href="Foreign-Function-Interface.html" accesskey="p" rel="prev">Foreign Function Interface</a>, Up: <a href="API-Reference.html" accesskey="u" rel="up">API Reference</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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<hr>
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<h3 class="section" id="Foreign-Objects-1"><span>6.20 Foreign Objects<a class="copiable-link" href="#Foreign-Objects-1"> ¶</a></span></h3>
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<a class="index-entry-id" id="index-foreign-object"></a>
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<p>This chapter contains reference information related to defining and
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working with foreign objects. See <a class="xref" href="Defining-New-Foreign-Object-Types.html">Defining New Foreign Object Types</a>,
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for a tutorial-like introduction to foreign objects.
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</p>
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<dl class="first-deftp">
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<dt class="deftp" id="index-scm_005ft_005fstruct_005ffinalize"><span class="category-def">C Type: </span><span><strong class="def-name">scm_t_struct_finalize</strong><a class="copiable-link" href="#index-scm_005ft_005fstruct_005ffinalize"> ¶</a></span></dt>
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<dd><p>This function type returns <code class="code">void</code> and takes one <code class="code">SCM</code>
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argument.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-scm_005fmake_005fforeign_005fobject_005ftype"><span class="category-def">C Function: </span><span><code class="def-type">SCM</code> <strong class="def-name">scm_make_foreign_object_type</strong> <code class="def-code-arguments">(SCM name, SCM slots, scm_t_struct_finalize finalizer)</code><a class="copiable-link" href="#index-scm_005fmake_005fforeign_005fobject_005ftype"> ¶</a></span></dt>
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<dd><p>Create a fresh foreign object type. <var class="var">name</var> is a symbol naming the
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type. <var class="var">slots</var> is a list of symbols, each one naming a field in the
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foreign object type. <var class="var">finalizer</var> indicates the finalizer, and may
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be <code class="code">NULL</code>.
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</p></dd></dl>
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<a class="index-entry-id" id="index-finalizer-1"></a>
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<a class="index-entry-id" id="index-finalization-1"></a>
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<p>We recommend that finalizers be avoided if possible. See <a class="xref" href="Foreign-Object-Memory-Management.html">Foreign Object Memory Management</a>. Finalizers must be async-safe and
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thread-safe. Again, see <a class="pxref" href="Foreign-Object-Memory-Management.html">Foreign Object Memory Management</a>. If you
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are embedding Guile in an application that is not thread-safe, and you
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define foreign object types that need finalization, you might want to
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disable automatic finalization, and arrange to call
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<code class="code">scm_manually_run_finalizers ()</code> yourself.
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</p>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-scm_005fset_005fautomatic_005ffinalization_005fenabled"><span class="category-def">C Function: </span><span><code class="def-type">int</code> <strong class="def-name">scm_set_automatic_finalization_enabled</strong> <code class="def-code-arguments">(int enabled_p)</code><a class="copiable-link" href="#index-scm_005fset_005fautomatic_005ffinalization_005fenabled"> ¶</a></span></dt>
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<dd><p>Enable or disable automatic finalization. By default, Guile arranges to
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invoke object finalizers automatically, in a separate thread if
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possible. Passing a zero value for <var class="var">enabled_p</var> will disable
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automatic finalization for Guile as a whole. If you disable automatic
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finalization, you will have to call <code class="code">scm_run_finalizers ()</code>
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periodically.
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</p>
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<p>Unlike most other Guile functions, you can call
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<code class="code">scm_set_automatic_finalization_enabled</code> before Guile has been
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initialized.
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</p>
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<p>Return the previous status of automatic finalization.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-scm_005frun_005ffinalizers"><span class="category-def">C Function: </span><span><code class="def-type">int</code> <strong class="def-name">scm_run_finalizers</strong> <code class="def-code-arguments">(void)</code><a class="copiable-link" href="#index-scm_005frun_005ffinalizers"> ¶</a></span></dt>
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<dd><p>Invoke any pending finalizers. Returns the number of finalizers that
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were invoked. This function should be called when automatic
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finalization is disabled, though it may be called if it is enabled as
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well.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-scm_005fassert_005fforeign_005fobject_005ftype"><span class="category-def">C Function: </span><span><code class="def-type">void</code> <strong class="def-name">scm_assert_foreign_object_type</strong> <code class="def-code-arguments">(SCM type, SCM val)</code><a class="copiable-link" href="#index-scm_005fassert_005fforeign_005fobject_005ftype"> ¶</a></span></dt>
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<dd><p>When <var class="var">val</var> is a foreign object of the given <var class="var">type</var>, do nothing.
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Otherwise, signal an error.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-scm_005fmake_005fforeign_005fobject_005f0"><span class="category-def">C Function: </span><span><code class="def-type">SCM</code> <strong class="def-name">scm_make_foreign_object_0</strong> <code class="def-code-arguments">(SCM type)</code><a class="copiable-link" href="#index-scm_005fmake_005fforeign_005fobject_005f0"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-scm_005fmake_005fforeign_005fobject_005f1"><span class="category-def">C Function: </span><span><code class="def-type">SCM</code> <strong class="def-name">scm_make_foreign_object_1</strong> <code class="def-code-arguments">(SCM type, void *val0)</code><a class="copiable-link" href="#index-scm_005fmake_005fforeign_005fobject_005f1"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-scm_005fmake_005fforeign_005fobject_005f2"><span class="category-def">C Function: </span><span><code class="def-type">SCM</code> <strong class="def-name">scm_make_foreign_object_2</strong> <code class="def-code-arguments">(SCM type, void *val0, void *val1)</code><a class="copiable-link" href="#index-scm_005fmake_005fforeign_005fobject_005f2"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-scm_005fmake_005fforeign_005fobject_005f3"><span class="category-def">C Function: </span><span><code class="def-type">SCM</code> <strong class="def-name">scm_make_foreign_object_3</strong> <code class="def-code-arguments">(SCM type, void *val0, void *val1, void *val2)</code><a class="copiable-link" href="#index-scm_005fmake_005fforeign_005fobject_005f3"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-scm_005fmake_005fforeign_005fobject_005fn"><span class="category-def">C Function: </span><span><code class="def-type">SCM</code> <strong class="def-name">scm_make_foreign_object_n</strong> <code class="def-code-arguments">(SCM type, size_t n, void *vals[])</code><a class="copiable-link" href="#index-scm_005fmake_005fforeign_005fobject_005fn"> ¶</a></span></dt>
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<dd><p>Make a new foreign object of the type with type <var class="var">type</var> and
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initialize the first <var class="var">n</var> fields to the given values, as appropriate.
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</p>
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<p>The number of fields for objects of a given type is fixed when the type
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is created. It is an error to give more initializers than there are
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fields in the value. It is perfectly fine to give fewer initializers
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than needed; this is convenient when some fields are of non-pointer
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types, and would be easier to initialize with the setters described
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below.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-scm_005fforeign_005fobject_005fref"><span class="category-def">C Function: </span><span><code class="def-type">void*</code> <strong class="def-name">scm_foreign_object_ref</strong> <code class="def-code-arguments">(SCM obj, size_t n);</code><a class="copiable-link" href="#index-scm_005fforeign_005fobject_005fref"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-scm_005fforeign_005fobject_005funsigned_005fref"><span class="category-def">C Function: </span><span><code class="def-type">scm_t_bits</code> <strong class="def-name">scm_foreign_object_unsigned_ref</strong> <code class="def-code-arguments">(SCM obj, size_t n);</code><a class="copiable-link" href="#index-scm_005fforeign_005fobject_005funsigned_005fref"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-scm_005fforeign_005fobject_005fsigned_005fref"><span class="category-def">C Function: </span><span><code class="def-type">scm_t_signed_bits</code> <strong class="def-name">scm_foreign_object_signed_ref</strong> <code class="def-code-arguments">(SCM obj, size_t n);</code><a class="copiable-link" href="#index-scm_005fforeign_005fobject_005fsigned_005fref"> ¶</a></span></dt>
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<dd><p>Return the value of the <var class="var">n</var>th field of the foreign object <var class="var">obj</var>.
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The backing store for the fields is as wide as a <code class="code">scm_t_bits</code>
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value, which is at least as wide as a pointer. The different variants
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handle casting in a portable way.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-scm_005fforeign_005fobject_005fset_005fx"><span class="category-def">C Function: </span><span><code class="def-type">void</code> <strong class="def-name">scm_foreign_object_set_x</strong> <code class="def-code-arguments">(SCM obj, size_t n, void *val);</code><a class="copiable-link" href="#index-scm_005fforeign_005fobject_005fset_005fx"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-scm_005fforeign_005fobject_005funsigned_005fset_005fx"><span class="category-def">C Function: </span><span><code class="def-type">void</code> <strong class="def-name">scm_foreign_object_unsigned_set_x</strong> <code class="def-code-arguments">(SCM obj, size_t n, scm_t_bits val);</code><a class="copiable-link" href="#index-scm_005fforeign_005fobject_005funsigned_005fset_005fx"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-scm_005fforeign_005fobject_005fsigned_005fset_005fx"><span class="category-def">C Function: </span><span><code class="def-type">void</code> <strong class="def-name">scm_foreign_object_signed_set_x</strong> <code class="def-code-arguments">(SCM obj, size_t n, scm_t_signed_bits val);</code><a class="copiable-link" href="#index-scm_005fforeign_005fobject_005fsigned_005fset_005fx"> ¶</a></span></dt>
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<dd><p>Set the value of the <var class="var">n</var>th field of the foreign object <var class="var">obj</var> to
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<var class="var">val</var>, after portably converting to a <code class="code">scm_t_bits</code> value, if
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needed.
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</p></dd></dl>
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<p>One can also access foreign objects from Scheme. See <a class="xref" href="Foreign-Objects-and-Scheme.html">Foreign Objects and Scheme</a>, for some examples.
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</p>
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<div class="example">
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<pre class="example-preformatted">(use-modules (system foreign-object))
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</pre></div>
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<dl class="first-deffn">
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<dt class="deffn" id="index-make_002dforeign_002dobject_002dtype"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">make-foreign-object-type</strong> <var class="def-var-arguments">name slots [#:finalizer=#f] [#:supers=’()]</var><a class="copiable-link" href="#index-make_002dforeign_002dobject_002dtype"> ¶</a></span></dt>
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<dd>
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<p>Make a new foreign object type. See the above documentation for
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<code class="code">scm_make_foreign_object_type</code>; these functions are exactly
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equivalent, except for the way in which the finalizer gets attached to
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instances (an internal detail), and the fact that this function accepts
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an optional list of superclasses, which will be paseed to
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<code class="code">make-class</code>.
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</p>
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<p>The resulting value is a GOOPS class. See <a class="xref" href="GOOPS.html">GOOPS</a>, for more on classes
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in Guile.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-define_002dforeign_002dobject_002dtype"><span class="category-def">Scheme Syntax: </span><span><strong class="def-name">define-foreign-object-type</strong> <var class="def-var-arguments">name constructor (slot ...) [#:finalizer=#f]</var><a class="copiable-link" href="#index-define_002dforeign_002dobject_002dtype"> ¶</a></span></dt>
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<dd><p>A convenience macro to define a type, using
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<code class="code">make-foreign-object-type</code>, and bind it to <var class="var">name</var>. A
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constructor will be bound to <var class="var">constructor</var>, and getters will be
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bound to each of <var class="var">slot...</var>.
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</p></dd></dl>
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Next: <a href="Smobs.html">Smobs</a>, Previous: <a href="Foreign-Function-Interface.html">Foreign Function Interface</a>, Up: <a href="API-Reference.html">API Reference</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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