38 lines
2.4 KiB
XML
38 lines
2.4 KiB
XML
<?xml version="1.0"?>
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<clause number="14.5.11" title="The typeof operator">
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<paragraph>The typeof operator is used to obtain the System.Type object for a type. <grammar_production><name><non_terminal where="14.5.11">typeof-expression</non_terminal></name> : <rhs><keyword>typeof</keyword><terminal>(</terminal><non_terminal where="11">type</non_terminal><terminal>)</terminal></rhs><rhs><keyword>typeof</keyword><terminal>(</terminal><keyword>void</keyword><terminal>)</terminal></rhs></grammar_production></paragraph>
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<paragraph>The first form of <non_terminal where="14.5.11">typeof-expression</non_terminal> consists of a typeof keyword followed by a parenthesized type. The result of an expression of this form is the System.Type object for the indicated type. There is only one System.Type object for any given type. <note>[Note: This means that for type T, typeof(T) == typeof(T) is always true. end note]</note> </paragraph>
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<paragraph>The second form of <non_terminal where="14.5.11">typeof-expression</non_terminal> consists of a typeof keyword followed by a parenthesized <keyword>void</keyword> keyword. The result of an expression of this form is the System.Type object that represents the absence of a type. The type object returned by typeof(<keyword>void</keyword>) is distinct from the type object returned for any type. </paragraph>
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<paragraph>
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<note>[Note: This special type object is useful in class libraries that allow reflection onto methods in the language, where those methods wish to have a way to represent the return type of any method, including <keyword>void</keyword> methods, with an instance of System.Type. end note]</note>
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</paragraph>
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<paragraph>
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<example>[Example: The example <code_example><![CDATA[
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using System;
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class Test
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{
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static void Main() {
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Type[] t = {
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typeof(int),
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typeof(System.Int32),
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typeof(string),
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typeof(double[]),
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typeof(void) };
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for (int i = 0; i < t.Length; i++) {
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Console.WriteLine(t[i].FullName);
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}
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}
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}
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]]></code_example>produces the following output: <code_example><![CDATA[
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System.Int32
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System.Int32
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System.String
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System.Double[]
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System.Void
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]]></code_example></example>
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</paragraph>
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<paragraph>
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<example>Note that <keyword>int</keyword> and System.Int32 are the same type. end example]</example>
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</paragraph>
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</clause>
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