40 lines
2.1 KiB
XML
40 lines
2.1 KiB
XML
<?xml version="1.0"?>
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<clause number="18.3.8" title="Constructors">
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<paragraph>Unlike a class, a struct is not permitted to declare a parameterless instance constructor. Instead, every struct implicitly has a parameterless instance constructor, which always returns the value that results from setting all value type fields to their default value and all reference type fields to null (<hyperlink>11.1.1</hyperlink>). A struct can declare instance constructors having parameters. <example>[Example: For example <code_example><![CDATA[
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struct Point
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{
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int x, y;
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public Point(int x, int y) {
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this.x = x;
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this.y = y;
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}
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}
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]]></code_example></example></paragraph>
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<paragraph>
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<example>Given the above declaration, the statements <code_example><![CDATA[
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Point p1 = new Point();
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Point p2 = new Point(0, 0);
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]]></code_example>both create a Point with x and y initialized to zero. end example]</example>
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</paragraph>
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<paragraph>A struct instance constructor is not permitted to include a constructor initializer of the form base(...). </paragraph>
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<paragraph>The this variable of a struct instance constructor corresponds to an out parameter of the struct type, and similar to an out parameter, this must be definitely assigned (<hyperlink>12.3</hyperlink>) at every location where the constructor returns. <example>[Example: Consider the instance constructor implementation below: <code_example><![CDATA[
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struct Point
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{
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int x, y;
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public int X {
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set { x = value; }
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}
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public int Y {
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set { y = value; }
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}
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public Point(int x, int y) {
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X = x; // error, this is not yet definitely assigned
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Y = y; // error, this is not yet definitely assigned
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}
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}
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]]></code_example></example></paragraph>
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<paragraph>
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<example>No instance member function (including the set accessors for the properties X and Y) can be called until all fields of the struct being constructed have been definitely assigned. Note, however, that if Point were a class instead of a struct, the instance constructor implementation would be permitted. end example]</example>
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</paragraph>
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</clause>
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