Help/Core/Nil.html

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  22 <p class="p1"><b>Nil</b></p>
  23 <p class="p2"><br></p>
  24 <p class="p3"><b>Inherits from: </b><a href="Object.html"><span class="s1"><b>Object</b></span></a><b><span class="Apple-converted-space"> </span></b></p>
  25 <p class="p2"><br></p>
  26 <p class="p3">Nil has a single instance named nil and is used to represent uninitialized data,</p>
  27 <p class="p3">bad values, or terminal values such as end-of-stream.</p>
  28 <p class="p2"><br></p>
  29 <p class="p4"><b>Instance Methods</b></p>
  30 <p class="p2"><br></p>
  31 <p class="p5"><b>isNil</b></p>
  32 <p class="p5"><span class="Apple-tab-span">     </span>Answers true because this <span class="s2">is</span> nil. In class Object this message is defined to answer false.</p>
  33 <p class="p6"><br></p>
  34 <p class="p5"><b>notNil</b></p>
  35 <p class="p5"><span class="Apple-tab-span">     </span>Answer false. In class Object this message answers true.</p>
  36 <p class="p6"><br></p>
  37 <p class="p5"><b>? anObject</b></p>
  38 <p class="p5"><span class="Apple-tab-span">     </span>? means return first non-nil argument. Since this IS nil then return anObject.</p>
  39 <p class="p5"><span class="Apple-tab-span">     </span>In class Object, ? is defined to answer the receiver.</p>
  40 <p class="p6"><br></p>
  41 <p class="p5"><b>?? aFunction</b></p>
  42 <p class="p5">If the receiver is nil, value the function and return the result.<span class="Apple-converted-space">  </span>Since this IS nil, then value the function and return the result. In class Object, ?? is defined to answer the receiver.</p>
  43 <p class="p6"><br></p>
  44 <p class="p5"><b>add(value)</b></p>
  45 <p class="p5">Returns an array with the <b>value</b>. This makes it unecessary to initialize when adding to a variable.</p>
  46 <p class="p6"><br></p>
  47 <p class="p5"><b>addAll(array)</b></p>
  48 <p class="p5">Returns an array with all the values. This makes it unecessary to initialize when adding to a variable.</p>
  49 <p class="p6"><br></p>
  50 <p class="p5"><b>remove</b></p>
  51 <p class="p5">Returns nil. This makes it unecessary to initialize when adding to a variable.</p>
  52 <p class="p6"><br></p>
  53 <p class="p5"><b>++ array</b></p>
  54 <p class="p5">Returns an array with all the values. This makes it unecessary to initialize when adding to a variable.</p>
  55 <p class="p2"><br></p>
  56 <p class="p4"><b>Dependancy</b></p>
  57 <p class="p2"><br></p>
  58 <p class="p3">All the messages for the Dependancy protocol (See class Object) are defined in class Nil<span class="Apple-converted-space"> </span></p>
  59 <p class="p3">to do nothing. This eliminates the need to check for nil when sending dependancy messages.</p>
  60 <p class="p2"><br></p>
  61 <p class="p4"><b>Other Methods</b></p>
  62 <p class="p2"><br></p>
  63 <p class="p3">Many other messages are defined in class Nil to do nothing. This eliminates the need to check for nil.</p>
  64 <p class="p2"><br></p>
  65 <p class="p2"><br></p>
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