<?xml version="1.0"?>
<clause number="17.10.6" title="Optional instance constructor parameters">
  <paragraph>
    <note>[Note: The this(...) form of constructor initializer is commonly used in conjunction with overloading to implement optional instance constructor parameters. In the example <code_example><![CDATA[
class Text  
{  
   public Text(): this(0, 0, null) {}  
   public Text(int x, int y): this(x, y, null) {}  
   public Text(int x, int y, string s) {  
      // Actual constructor implementation  
   }  
}  
]]></code_example>the first two instance constructors merely provide the default values for the missing arguments. Both use a this(...) constructor initializer to invoke the third instance constructor, which actually does the work of initializing the new instance. The effect is that of optional constructor parameters: <code_example><![CDATA[
Text t1 = new Text();          // Same as Text(0, 0, null)  
Text t2 = new Text(5, 10);       // Same as Text(5, 10, null)  
Text t3 = new Text(5, 20, "Hello");  
]]></code_example>end note]</note>
  </paragraph>
</clause>
