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<a href="00067.html" target="topic">12.4 约束块</a></div>
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12.4.7 迭代约束</div>
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迭代约束让我们能够使用循环变量和索引表达式以一种参数化的方式约束数组变量。 </p>
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定义一个迭代约束的语法如下： </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00418"><pre class="Element12">constraint_expression ::= <span style="color: #008000">// 引用自附录A.1.9</span>
...
| <strong><span style="color: #FF0000">foreach (</span></strong>array_identifier <strong><span style="color: #FF0000">[</span></strong>loop_variables<strong><span style="color: #FF0000">])</span></strong> constraint_set
loop_variables ::= [index_variable_identifier] {<strong><span style="color: #FF0000">,</span></strong> [index_variable_identifier]}
<span style="color: #008000">// 引用自附录A.6.8</span></pre></div></div>
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<strong>语法12-6 — foreach迭代约束语法（摘录自附录A）</strong></p><p class="Element10">
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<span style="color: #0000FF">foreach</span>结构指定了数组元素上的迭代。它的参数是一个标识符跟着一个包围在方括号中的循环变量，这个标识符说明了任意类型的数组（固定尺寸、动态数组、联合数组、或队列）。每一个循环变量均对应于数组的某一维。 </p>
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例如： </p><div class="Element170">
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<div class="Element13"><div class="Element12" id="code00419"><pre class="Element12"><span style="color: #0000FF">class</span> C<span style="color: #800080">;</span>
<span style="color: #0000FF">rand byte</span> A<span style="color: #800080">[];</span>
<span style="color: #0000FF">constraint</span> C1 <span style="color: #800080">{</span><span style="color: #0000FF">foreach</span> <span style="color: #800080">(</span>A<span style="color: #800080">[</span>i<span style="color: #800080">])</span> A<span style="color: #800080">[</span>i<span style="color: #800080">]</span> <span style="color: #0000FF">inside</span> <span style="color: #800080">{</span><span style="color: #FF0000">2</span><span style="color: #800080">,</span><span style="color: #FF0000">4</span><span style="color: #800080">,</span><span style="color: #FF0000">8</span><span style="color: #800080">,</span><span style="color: #FF0000">16</span><span style="color: #800080">};}</span>
<span style="color: #0000FF">constraint</span> C2 <span style="color: #800080">{</span><span style="color: #0000FF">foreach</span> <span style="color: #800080">(</span>A<span style="color: #800080">[</span>j<span style="color: #800080">])</span> A<span style="color: #800080">[</span>j<span style="color: #800080">]</span> <span style="color: #800080">> </span><span style="color: #FF0000">2</span><span style="color: #800080">*</span>j<span style="color: #800080">;}</span>
<span style="color: #0000FF">endclass</span></pre></div></div>
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<i>C1</i>将数组<i>A</i>的每一个元素约束成位于集合<span style="color: #800080">[</span><span style="color: #FF0000">2</span><span style="color: #800080">,</span><span style="color: #FF0000">4</span><span style="color: #800080">,</span><span style="color: #FF0000">8</span><span style="color: #800080">,</span><span style="color: #FF0000">16</span><span style="color: #800080">]</span>之内。<i>C2</i>将数组<i>A</i>中的每一个元素约束成大于其索引值的两倍。 </p>
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循环变量的数目不能超过数组变量的维数。每一个循环变量的作用范围是<span style="color: #0000FF">foreach</span>约束结构，包括它的<i>constraint_set</i>。每一个循环变量的类型被隐含地声明成与数组索引类型一致。一个空的循环变量指示在数组的该维上没有迭代。与缺省参数一样，尾部的逗号列表可以被忽略，因此，<span style="color: #0000FF">foreach</span><span style="color: #800080">(</span>arr<span style="color: #800080">[</span>j<span style="color: #800080">])</span>等价于<span style="color: #0000FF">foreach</span><span style="color: #800080">(</span>arr<span style="color: #800080">[</span>j<span style="color: #800080">, , , ,])</span>。任何循环变量都不能与数组具有相同的标识符。 </p>
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循环变量与数组索引的映射由维基数确定，参见<a href="00287.html" target="topic">23.7节</a>。 </p><div class="Element170">
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