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<html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8" /><title>Hyperlinked ECMA C# Language Specification</title><meta name="author" content="Jon Jagger" /><link rel="stylesheet" href="ecma334.css"></link></head><body><div align="right"><em><a href="http://www.jaggersoft.com">Jon Jagger</a></em></div><div align="right"><a href="mailto:[e-mail]">[e-mail]</a></div><form method="get" action="http://search.atomz.com/search/"><input size="30" name="sp-q"></input><input type="submit" value="Search C# Spec"></input><input type="hidden" name="sp-a" value="sp10024177"></input><input type="hidden" name="sp-f" value="ISO-8859-1"></input></form><a href="toc.htm">Table of Contents</a> <a href="1.htm">1</a> <a href="2.htm">2</a> <a href="3.htm">3</a> <a href="4.htm">4</a> <a href="5.htm">5</a> <a href="6.htm">6</a> <a href="7.htm">7</a> <a href="8.htm">8</a> <a href="9.htm">9</a> <a href="10.htm">10</a> <a href="11.htm">11</a> <a href="12.htm">12</a> <a href="13.htm">13</a> <a href="14.htm">14</a> <a href="15.htm">15</a> <a href="16.htm">16</a> <a href="17.htm">17</a> <a href="18.htm">18</a> <a href="19.htm">19</a> <a href="20.htm">20</a> <a href="21.htm">21</a> <a href="22.htm">22</a> <a href="23.htm">23</a> <a href="24.htm">24</a> <a href="25.htm">25</a> <a href="notes.htm">Notes</a> <a href="HyperlinkedCSharpECMA.zip">Download</a><span class="ruler"></span><span class="heading">ECMA-334 C# Language Specification</span><span class="navigate"><a href="8.1.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="8.2.1.htm"><img src="next.gif" alt="next" border="0" /></a></span><span class="clause-depth"><a href="7.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="9.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="8.htm">8</a></span><span class="clause-title-previous"> Language Overview</span></span><span class="clause-depth"><a href="8.1.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="8.3.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">8.2</span><span class="clause-title"> Types</span></span><span class="informative"><span class="paragraph">C# supports two kinds of types: value types and reference types. Value types include simple types (e.g., <span class="keyword">char</span>, <span class="keyword">int</span>, and <span class="keyword">float</span>), enum types, and struct types. Reference types include class types, interface types, delegate types, and array types. </span><span class="paragraph">Value types differ from reference types in that variables of the value types directly contain their data, whereas variables of the reference types store references to objects. With reference types, it is possible for two variables to reference the same object, and thus possible for operations on one variable to affect the object referenced by the other variable. With value types, the variables each have their own copy of the data, and it is not possible for operations on one to affect the other. </span><span class="paragraph">The example <pre class="code-example">
using System;  
class Class1  
{  
   public int Value = 0;  
}  
class Test  
{  
   static void Main() {  
      int val1 = 0;  
      int val2 = val1;  
      val2 = 123;  
      Class1 ref1 = new Class1();  
      Class1 ref2 = ref1;  
      ref2.Value = 123;  
      Console.WriteLine("Values: {0}, {1}", val1, val2);  
      Console.WriteLine("Refs: {0}, {1}", ref1.Value, ref2.Value);  
   }  
}  
</pre>shows this difference. The output produced is <pre class="code-example">
Values: 0, 123  
Refs: 123, 123  
</pre></span><span class="paragraph">The assignment to the local variable val1 does not impact the local variable val2 because both local variables are of a value type (the type <span class="keyword">int</span>) and each local variable of a value type has its own storage. In contrast, the assignment ref2.Value = 123; affects the object that both ref1 and ref2 reference. </span><span class="paragraph">The lines <pre class="code-example">
Console.WriteLine("Values: {0}, {1}", val1, val2);  
Console.WriteLine("Refs: {0}, {1}", ref1.Value, ref2.Value);  
</pre>deserve further comment, as they demonstrate some of the string formatting behavior of Console.WriteLine, which, in fact, takes a variable number of arguments. The first argument is a string, which may contain numbered placeholders like {0} and {1}. Each placeholder refers to a trailing argument with {0} referring to the second argument, {1} referring to the third argument, and so on. Before the output is sent to the console, each placeholder is replaced with the formatted value of its corresponding argument. </span><span class="paragraph">Developers can define new value types through enum and struct declarations, and can define new reference types via class, interface, and delegate declarations. The example <pre class="code-example">
using System;  
public enum Color  
{  
   Red, Blue, Green  
}  
public struct Point   
{   
   public int x, y;   
}  
public interface IBase  
{  
   void F();  
}  
public interface IDerived: IBase  
{  
   void G();  
}  
public class A  
{  
   protected virtual void H() {  
      Console.WriteLine("A.H");  
   }  
}  
public class B: A, IDerived   
{  
   public void F() {  
      Console.WriteLine("B.F, implementation of IDerived.F");  
   }  
   public void G() {  
      Console.WriteLine("B.G, implementation of IDerived.G");  
   }  
   override protected void H() {  
      Console.WriteLine("B.H, override of A.H");  
   }  
}  
public delegate void EmptyDelegate();  
</pre>shows an example of each kind of type declaration. Later sections describe type declarations in detail. </span></span><span class="ruler"></span><table><tr><td><table align="left" bgcolor="navy"><tr bgcolor="navy"><td><font face="Arial,sans-serif" size="6" color="yellow"><strong>{ JSL }</strong></font></td></tr></table></td></tr><tr><td><font face="Arial,sans-serif" size="2" color="navy"><strong>Jagger Software Ltd</strong></font></td></tr><tr><td><font face="Arial,sans-serif" size="2" color="navy"><strong>Company # 4070126</strong></font></td></tr><tr><td><font face="Arial,sans-serif" size="2" color="navy"><strong>VAT # 762 5213 42</strong></font></td></tr></table><img src="valid-html401.png" align="left" height="31" width="88" alt="Valid HTML 4.01" /><img src="vcss.gif" align="left" height="31" width="88" alt="Valid CSS" /></body></html>