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10.10.6 Optional instance constructor parameters

Visual Studio .NET 2003

The this(...) form of constructor initializer is commonly used in conjunction with overloading to implement optional instance constructor parameters. In the example

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

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:

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");