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<div class="section" id="memory-management-glossary-u">
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<span id="glossary-u"></span><h1>Memory Management Glossary: U<a class="headerlink" href="#memory-management-glossary-u" title="Permalink to this headline">¶</a></h1>
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<p class="glossary-alphabet"><a class="reference internal" href="a.html#glossary-a"><em>A</em></a>
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| <a class="reference internal" href="b.html#glossary-b"><em>B</em></a>
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| <a class="reference internal" href="c.html#glossary-c"><em>C</em></a>
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| <a class="reference internal" href="d.html#glossary-d"><em>D</em></a>
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| <a class="reference internal" href="e.html#glossary-e"><em>E</em></a>
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| <a class="reference internal" href="f.html#glossary-f"><em>F</em></a>
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| <a class="reference internal" href="g.html#glossary-g"><em>G</em></a>
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| <a class="reference internal" href="h.html#glossary-h"><em>H</em></a>
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| <a class="reference internal" href="i.html#glossary-i"><em>I</em></a>
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| J
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| <a class="reference internal" href="k.html#glossary-k"><em>K</em></a>
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| <a class="reference internal" href="l.html#glossary-l"><em>L</em></a>
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| <a class="reference internal" href="m.html#glossary-m"><em>M</em></a>
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| <a class="reference internal" href="n.html#glossary-n"><em>N</em></a>
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| <a class="reference internal" href="o.html#glossary-o"><em>O</em></a>
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| <a class="reference internal" href="p.html#glossary-p"><em>P</em></a>
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| <a class="reference internal" href="q.html#glossary-q"><em>Q</em></a>
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| <a class="reference internal" href="r.html#glossary-r"><em>R</em></a>
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| <a class="reference internal" href="s.html#glossary-s"><em>S</em></a>
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| <a class="reference internal" href="t.html#glossary-t"><em>T</em></a>
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| <a class="reference internal" href="#glossary-u"><em>U</em></a>
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| <a class="reference internal" href="v.html#glossary-v"><em>V</em></a>
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| <a class="reference internal" href="w.html#glossary-w"><em>W</em></a>
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| X
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| Y
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| <a class="reference internal" href="z.html#glossary-z"><em>Z</em></a></p>
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<dl class="glossary docutils">
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<dt id="term-unaligned">unaligned</dt>
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<dd><div class="admonition-also-known-as first admonition">
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<p class="first admonition-title">Also known as</p>
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<p class="last"><em>misaligned</em>.</p>
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</div>
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<p>An <a class="reference internal" href="a.html#term-address"><em class="xref std std-term">address</em></a> is unaligned or misaligned if it does not
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comply with some <a class="reference internal" href="a.html#term-alignment"><em class="xref std std-term">alignment</em></a> constraint on it.</p>
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<p>For example, typically double precision floating point numbers
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occupy 8 <a class="reference internal" href="b.html#term-byte-1"><em class="xref std std-term">byte<sup>(1)</sup></em></a> and have an alignment of 4 bytes;
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that is, their address must be a multiple of four. If a
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program tries to access such a number using an address that is
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not a multiple of four, a <a class="reference internal" href="b.html#term-bus-error"><em class="xref std std-term">bus error</em></a> may result,
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depending on the processor architecture and instruction used.</p>
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<div class="admonition-opposite-term admonition">
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<p class="first admonition-title">Opposite term</p>
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<p class="last"><a class="reference internal" href="a.html#term-alignment"><em class="xref std std-term">aligned</em></a>.</p>
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</div>
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<div class="admonition-see-also last admonition seealso">
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<p class="first admonition-title">See also</p>
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<p class="last"><a class="reference internal" href="a.html#term-alignment"><em class="xref std std-term">alignment</em></a>, <a class="reference internal" href="b.html#term-bus-error"><em class="xref std std-term">bus error</em></a>.</p>
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</div>
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</dd>
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<dt id="term-unboxed">unboxed</dt>
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<dd><p class="first">Unboxed <a class="reference internal" href="o.html#term-object"><em class="xref std std-term">objects</em></a> are represented by an
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encoding of the data itself, and not by a <a class="reference internal" href="p.html#term-pointer"><em class="xref std std-term">pointer</em></a> to
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that data.</p>
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<p>Representations are typically chosen so that unboxed values
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are the same size as the pointer part of a <a class="reference internal" href="b.html#term-boxed"><em class="xref std std-term">boxed</em></a>
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object. Sometimes the value is <a class="reference internal" href="t.html#term-tag"><em class="xref std std-term">tagged</em></a> to
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distinguish it from a boxed object. The entire object is
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duplicated when the object is passed around, so updates to it,
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if allowed, only affect one copy.</p>
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<div class="admonition-similar-term admonition">
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<p class="first admonition-title">Similar term</p>
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<p class="last"><a class="reference internal" href="i.html#term-immediate-data"><em class="xref std std-term">immediate data</em></a>.</p>
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</div>
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<div class="admonition-opposite-term admonition">
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<p class="first admonition-title">Opposite term</p>
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<p class="last"><a class="reference internal" href="b.html#term-boxed"><em class="xref std std-term">boxed</em></a>.</p>
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</div>
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<div class="admonition-related-publication last admonition">
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<p class="first admonition-title">Related publication</p>
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<p class="last"><a class="reference internal" href="../mmref/bib.html#gudeman93"><em>Gudeman (1993)</em></a>.</p>
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</div>
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</dd>
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<dt id="term-unclamped-state">unclamped state</dt>
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<dd><div class="admonition-in-the-mps first last admonition">
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<p class="first admonition-title">In the MPS</p>
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<p class="last">One of the three states an <a class="reference internal" href="a.html#term-arena"><em class="xref std std-term">arena</em></a> can be in (the
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others being the <a class="reference internal" href="c.html#term-clamped-state"><em class="xref std std-term">clamped state</em></a> and the
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<a class="reference internal" href="p.html#term-parked-state"><em class="xref std std-term">parked state</em></a>). In the unclamped state, object
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motion and other background activity may occur. Call
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<a class="reference internal" href="../topic/arena.html#mps_arena_release" title="mps_arena_release"><tt class="xref c c-func docutils literal"><span class="pre">mps_arena_release()</span></tt></a> to put an arena into the
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unclamped state.</p>
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</div>
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</dd>
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<dt id="term-undead">undead</dt>
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<dd><p class="first">An undead object is an <a class="reference internal" href="o.html#term-object"><em class="xref std std-term">object</em></a> that cannot be proven to
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be <a class="reference internal" href="d.html#term-dead"><em class="xref std std-term">dead</em></a> by the <a class="reference internal" href="g.html#term-garbage-collector"><em class="xref std std-term">garbage collector</em></a>, but whose
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<a class="reference internal" href="l.html#term-live"><em class="xref std std-term">liveness</em></a> is dubious.</p>
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<p class="last">For example, an <a class="reference internal" href="a.html#term-ambiguous-reference"><em class="xref std std-term">ambiguous reference</em></a> to an object on a
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<a class="reference internal" href="p.html#term-page"><em class="xref std std-term">page</em></a> may mark the entire page as <a class="reference internal" href="r.html#term-reachable"><em class="xref std std-term">reachable</em></a>. No
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further data is collected about that page. The other objects
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on the page will survive, even though their reachability has
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not been determined. They are <em>undead</em>.</p>
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</dd>
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<dt id="term-unmapped">unmapped</dt>
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<dd><div class="admonition-also-known-as first admonition">
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<p class="first admonition-title">Also known as</p>
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<p class="last"><em>free</em>.</p>
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</div>
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<p>A range of <a class="reference internal" href="v.html#term-virtual-address"><em class="xref std std-term">virtual addresses</em></a> is said
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to be <em>unmapped</em> (<em>free</em> on Windows) if there is no
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<a class="reference internal" href="p.html#term-physical-memory-2"><em class="xref std std-term">physical memory<sup>(2)</sup></em></a> associated with the range.</p>
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<p>An unmapped range may or may not be <a class="reference internal" href="r.html#term-reserved"><em class="xref std std-term">reserved</em></a>.</p>
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<div class="admonition-opposite-term last admonition">
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<p class="first admonition-title">Opposite term</p>
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<p class="last"><a class="reference internal" href="m.html#term-mapped"><em class="xref std std-term">mapped</em></a>.</p>
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</div>
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</dd>
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<dt id="term-unreachable">unreachable</dt>
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<dd><p class="first">An <a class="reference internal" href="o.html#term-object"><em class="xref std std-term">object</em></a> is unreachable if there is no
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<a class="reference internal" href="r.html#term-reference"><em class="xref std std-term">reference</em></a> chain to it from any <a class="reference internal" href="r.html#term-root"><em class="xref std std-term">root</em></a>.</p>
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<p>An object will become unreachable when the <a class="reference internal" href="m.html#term-mutator"><em class="xref std std-term">mutator</em></a>
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overwrites its last (direct or indirect) reference to the
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object.</p>
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<div class="admonition-similar-term admonition">
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<p class="first admonition-title">Similar term</p>
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<p class="last"><a class="reference internal" href="d.html#term-dead"><em class="xref std std-term">dead</em></a>.</p>
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</div>
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<div class="admonition-opposite-term admonition">
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<p class="first admonition-title">Opposite terms</p>
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<p class="last"><a class="reference internal" href="r.html#term-reachable"><em class="xref std std-term">reachable</em></a>, <a class="reference internal" href="l.html#term-live"><em class="xref std std-term">live</em></a>.</p>
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</div>
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<div class="admonition-see-also last admonition seealso">
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<p class="first admonition-title">See also</p>
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<p class="last"><a class="reference internal" href="r.html#term-reachable"><em class="xref std std-term">reachable</em></a>, <a class="reference internal" href="g.html#term-garbage-collection"><em class="xref std std-term">garbage collection</em></a>.</p>
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</div>
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</dd>
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<dt id="term-unsure-reference">unsure reference</dt>
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<dd><div class="admonition-see first last admonition">
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<p class="first admonition-title">See</p>
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<p class="last"><a class="reference internal" href="a.html#term-ambiguous-reference"><em class="xref std std-term">ambiguous reference</em></a>.</p>
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</div>
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</dd>
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<dt id="term-unwrapped">unwrapped</dt>
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<dd><div class="admonition-also-known-as first admonition">
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<p class="first admonition-title">Also known as</p>
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<p class="last"><em>raw</em>.</p>
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</div>
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<p>A value is <em>unwrapped</em> or <em>raw</em> if it is not encoded with type
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information.</p>
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<p>In a dynamically-typed language, the compiler may sometimes be
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able to pick a more compact or efficient representation for a
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value if it can prove that the type can be determined at
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compile-time. This is a particularly useful optimization for
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numeric values such as integers or floats.</p>
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<div class="admonition-opposite-term admonition">
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<p class="first admonition-title">Opposite term</p>
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<p class="last"><a class="reference internal" href="w.html#term-wrapped"><em class="xref std std-term">wrapped</em></a>.</p>
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</div>
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<div class="admonition-see-also admonition seealso">
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<p class="first admonition-title">See also</p>
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<p class="last"><a class="reference internal" href="b.html#term-boxed"><em class="xref std std-term">boxed</em></a>, <a class="reference internal" href="t.html#term-tag"><em class="xref std std-term">tag</em></a>, <a class="reference internal" href="v.html#term-value-object"><em class="xref std std-term">value object</em></a>.</p>
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</div>
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<div class="admonition-related-publication last admonition">
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<p class="first admonition-title">Related publication</p>
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<p class="last"><a class="reference internal" href="../mmref/bib.html#gudeman93"><em>Gudeman (1993)</em></a>.</p>
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</div>
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</dd>
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<dt id="term-use-after-free">use after free</dt>
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<dd><div class="admonition-see first last admonition">
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<p class="first admonition-title">See</p>
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<p class="last"><a class="reference internal" href="p.html#term-premature-free"><em class="xref std std-term">premature free</em></a>.</p>
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</div>
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</dd>
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<a href="http://www.ravenbrook.com/project/mps/release/1.111.0/">MPS Kit release 1.111.0</a><br>
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<a href="http://www.ravenbrook.com/project/mps/release/">All MPS Kit releases</a>
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