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<title>Instances (Guile Reference Manual)</title>
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<div class="subsection-level-extent" id="Instances">
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Next: <a href="Slots.html" accesskey="n" rel="next">Slots</a>, Previous: <a href="Classes.html" accesskey="p" rel="prev">Classes</a>, Up: <a href="Introspection.html" accesskey="u" rel="up">Introspection</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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<h4 class="subsection" id="Instances-1"><span>8.8.2 Instances<a class="copiable-link" href="#Instances-1"> ¶</a></span></h4>
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<dl class="first-deffn">
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<dt class="deffn" id="index-class_002dof"><span class="category-def">primitive procedure: </span><span><strong class="def-name">class-of</strong> <var class="def-var-arguments">value</var><a class="copiable-link" href="#index-class_002dof"> ¶</a></span></dt>
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<dd><p>Return the GOOPS class of any Scheme <var class="var">value</var>.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-instance_003f"><span class="category-def">primitive procedure: </span><span><strong class="def-name">instance?</strong> <var class="def-var-arguments">object</var><a class="copiable-link" href="#index-instance_003f"> ¶</a></span></dt>
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<dd><p>Return <code class="code">#t</code> if <var class="var">object</var> is any GOOPS instance, otherwise
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<code class="code">#f</code>.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-is_002da_003f"><span class="category-def">procedure: </span><span><strong class="def-name">is-a?</strong> <var class="def-var-arguments">object class</var><a class="copiable-link" href="#index-is_002da_003f"> ¶</a></span></dt>
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<dd><p>Return <code class="code">#t</code> if <var class="var">object</var> is an instance of <var class="var">class</var> or one of
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its subclasses.
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</p></dd></dl>
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<p>You can use the <code class="code">is-a?</code> predicate to ask whether any given value
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belongs to a given class, or <code class="code">class-of</code> to discover the class of a
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given value. Note that when GOOPS is loaded (by code using the
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<code class="code">(oop goops)</code> module) built-in classes like <code class="code"><string></code>,
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<code class="code"><list></code> and <code class="code"><number></code> are automatically set up,
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corresponding to all Guile Scheme types.
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(is-a? 2.3 <number>) ⇒ #t
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(is-a? 2.3 <real>) ⇒ #t
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(is-a? 2.3 <string>) ⇒ #f
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(is-a? '("a" "b") <string>) ⇒ #f
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(is-a? '("a" "b") <list>) ⇒ #t
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(is-a? (car '("a" "b")) <string>) ⇒ #t
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(is-a? <string> <class>) ⇒ #t
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(is-a? <class> <string>) ⇒ #f
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(class-of 2.3) ⇒ #<<class> <real> 908c708>
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(class-of #(1 2 3)) ⇒ #<<class> <vector> 908cd20>
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(class-of <string>) ⇒ #<<class> <class> 8bd3e10>
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(class-of <class>) ⇒ #<<class> <class> 8bd3e10>
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</pre></div>
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