doc/guide/localhost/MLtonWeak

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  26 <h1>MLtonWeak</h1>
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  29 <div id="preamble">
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  32 <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">MLTON_WEAK</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
  33 <span class="w">   </span><span class="k">sig</span><span class="w"></span>
  34 <span class="w">      </span><span class="k">type</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
  35
  36 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">get</span><span class="p">:</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">option</span><span class="w"></span>
  37 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">new</span><span class="p">:</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">&#39;a</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
  38 <span class="w">   </span><span class="k">end</span><span class="w"></span>
  39 </pre></div></div></div>
  40 <div class="paragraph"><p>A weak pointer is a pointer to an object that is nulled if the object
  41 becomes <a href="Reachability">unreachable</a> due to garbage collection.  The
  42 weak pointer does not itself cause the object it points to be retained
  43 by the garbage collector&#8201;&#8212;&#8201;only other strong pointers can do that.
  44 For objects that are not allocated in the heap, like integers, a weak
  45 pointer will always be nulled.  So, if <span class="monospaced">w: int Weak.t</span>, then
  46 <span class="monospaced">Weak.get w = NONE</span>.</p></div>
  47 <div class="ulist"><ul>
  48 <li>
  49 <p>
  50 <span class="monospaced">type 'a t</span>
  51 </p>
  52 <div class="paragraph"><p>the type of weak pointers to objects of type <span class="monospaced">'a</span></p></div>
  53 </li>
  54 <li>
  55 <p>
  56 <span class="monospaced">get w</span>
  57 </p>
  58 <div class="paragraph"><p>returns <span class="monospaced">NONE</span> if the object pointed to by <span class="monospaced">w</span> no longer exists.
  59 Otherwise, returns <span class="monospaced">SOME</span> of the object pointed to by <span class="monospaced">w</span>.</p></div>
  60 </li>
  61 <li>
  62 <p>
  63 <span class="monospaced">new x</span>
  64 </p>
  65 <div class="paragraph"><p>returns a weak pointer to <span class="monospaced">x</span>.</p></div>
  66 </li>
  67 </ul></div>
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