help/info/omit.html

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  32 <h1>omit</h1>
  33 <hr align="left" width="75%">
  34 <p>The <code>omit</code> keyword denotes the missing value. The <code>omit</code> can only be assigned to optional fields of <code>record</code> and <code>set</code> types to indicate that an
  35 optional field is not present.
  36 <hr align="left" width="50%">
  37 <p>Related keywords:</p>
  38 <ul>
  39   <li><a href="optional.html"><b><font face="Courier New" color="#003258" size="4">optional</font></b></a></li>
  40   <li><a href="record.html"><b><font face="Courier New" color="#003258" size="4">record</font></b></a></li>
  41   <li><a href="set.html"><b><font face="Courier New" color="#003258" size="4">set</font></b></a></li>
  42 </ul>
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  44 <div align="center">
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  47   <tr>
  48     <td width="100%">
  49     <h3 align="center"><font face="Courier New" color="#003258" size="5"><b>omit</b></font></h3>
  50     </td>
  51   </tr>
  52 </table>
  53 </center>
  54 </div>
  55 <hr align="left" width="25%">
  56 Example:
  57 <p><code> module m {<br>
  58 type record R { integer field1 optional, boolean field2 }<br>
  59 type set S { integer field1 optional, boolean field2 }<br>
  60 <br>
  61 control {<br>
  62 var R r1 := { omit, false };<br>
  63 var S s1 := { field1 := omit, field2 := true };<br>
  64 var S s2;<br>
  65 <br>
  66 s2.field1 := omit;<br>
  67 s2.field2 := false;<br>
  68 }<br>
  69 } </code>
  70 <p>Both type S and R contain an optional field1 element. Variable r1 is initialized using the value list notation; the optional field is omitted. Variable s1 is initialized using the value
  71 assignment notation; the optional field1 is not present. Finally, variable s2 is not initialized. Its fields are set via normal assignments through field references (i.e. using the dot notation);
  72 field1 is absent, again.
  73 <hr align="left" width="25%">
  74 <p><a HREF="BNF.html#omitvalue">BNF definition</a> of <font face="Courier New">omit</font></p>
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