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<a href="#" onmousedown="showPopup(this, 'popup00200');"><img src="seealsolink.png" border="0" alt="" title=""></a> SystemVerilog 3.1a语言参考手册</div>
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11.12 继承与子类</div>
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前一节定义了一个称为<i>Packet</i>的类。我们可以扩展这个类以便使<i>packet</i>串接在一起形成一个链表。一种解决方案是产生一个新的被称为<i>LinkedPacket</i>的类，它包含一个类型为<i>Packet</i>的变量：<i>packet_c</i>。 </p>
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为了引用<i>Packet</i>类属性，需要引用变量<i>packet_c</i>。 </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00362"><pre class="Element12"><span style="color: #0000FF">class</span> LinkedPacket<span style="color: #800080">;</span>
Packet packet_c<span style="color: #800080">;</span>
LinkedPacket next<span style="color: #800080">;</span>
<span style="color: #0000FF">function</span> LinkedPacket get_next<span style="color: #800080">();</span>
get_next <span style="color: #800080">=</span> next<span style="color: #800080">;</span>
<span style="color: #0000FF">endfunction</span>
<span style="color: #0000FF">endclass</span></pre></div></div>
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由于<i>LinkedPacket</i>是<i>Packet</i>的一个特例，所以一个更合理的解决方案是扩展<i>Packet</i>类以便产生一个新的子类，这个子类继承父类的成员。例如： </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00363"><pre class="Element12"><span style="color: #0000FF">class</span> LinkedPacket <span style="color: #0000FF">extends</span> Packet<span style="color: #800080">;</span>
LinkedPacket next<span style="color: #800080">;</span>
<span style="color: #0000FF">function</span> LinkedPacket get_next<span style="color: #800080">();</span>
get_next <span style="color: #800080">=</span> next<span style="color: #800080">;</span>
<span style="color: #0000FF">endfunction</span>
<span style="color: #0000FF">endclass</span></pre></div></div>
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现在，<i>Packet</i>的所有方法和类成员都是<i>LinkedPacket</i>的一部分，就好像它们在<i>LinkedPacket</i>中定义一样，并且<i>LinkedPacket</i>具有额外的类属性和方法。 </p>
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父类的方法也可以被过载，这样就可以改变它们的定义。 </p>
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SystemVerilog所提供的机制被称为单继承，也就是说，每一个子类都由一个单一的父类继承而来。</p></div>
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