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📁 This ECMA Standard specifies the form and establishes the interpretation of programs written in the
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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:jon@jaggersoft.com">jon@jaggersoft.com</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="8.11.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="8.13.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="8.11.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="8.13.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">8.12</span><span class="clause-title"> Namespaces and assemblies</span></span><span class="informative"><span class="paragraph">The programs presented so far have stood on their own except for dependence on a few system-provided classes such as System.Console. It is far more common, however, for real-world applications to consist of several different pieces, each compiled separately. For example, a corporate application might depend on several different components, including some developed internally and some purchased from independent software vendors. </span><span class="paragraph">Namespaces and assemblies enable this component-based system. Namespaces provide a logical organizational system. Namespaces are used both as an "internal" organization system for a program, and as an "external" organization system-a way of presenting program elements that are exposed to other programs. </span><span class="paragraph">Assemblies are used for physical packaging and deployment. An assembly may contain types, the executable code used to implement these types, and references to other assemblies. </span><span class="paragraph">To demonstrate the use of namespaces and assemblies, this section revisits the "hello, world" program presented earlier, and splits it into two pieces: a class library that provides messages and a console application that displays them. </span><span class="paragraph">The class library will contain a single class named HelloMessage. The example <pre class="code-example">
// HelloLibrary.cs  
namespace CSharp.Introduction  
{  
   public class HelloMessage  
   {  
      public string Message {  
         get {  
            return "hello, world";  
         }  
      }  
   }  
}  
</pre>shows the HelloMessage class in a namespace named CSharp.Introduction. The HelloMessage class provides a read-only property named Message. Namespaces can nest, and the declaration <pre class="code-example">
namespace CSharp.Introduction  
{...}  
</pre>is shorthand for two levels of namespace nesting: <pre class="code-example">
namespace CSharp  
{  
   namespace Introduction  
   {...}  
}   
</pre></span><span class="paragraph">The next step in the componentization of "hello, world" is to write a console application that uses the HelloMessage class. The fully qualified name for the  class-CSharp.Introduction.HelloMessage-could be used, but this name is quite <span class="keyword">long</span> and unwieldy. An easier way is to use a using namespace directive, which makes it possible to use all of the types in a namespace without qualification. The example <pre class="code-example">
// HelloApp.cs  
using CSharp.Introduction;  
class HelloApp  
{  
   static void Main() {  
      HelloMessage m = new HelloMessage();  
      System.Console.WriteLine(m.Message);  
   }  
}  
</pre>shows a using namespace directive that refers to the CSharp.Introduction namespace. The occurrences of HelloMessage are shorthand for CSharp.Introduction.HelloMessage. </span><span class="paragraph">C# also enables the definition and use of aliases. A using alias directive defines an alias for a type. Such aliases can be useful in situation in which name collisions occur between two class libraries, or when a small number of types from a much larger namespace are being used. The example <pre class="code-example">
using MessageSource = CSharp.Introduction.HelloMessage;  
</pre>shows a using alias directive that defines MessageSource as an alias for the HelloMessage class. </span><span class="paragraph">The code we have written can be compiled into a class library containing the class HelloMessage and an application containing the class HelloApp. The details of this compilation step might differ based on the compiler or tool being used. A command-line compiler might enable compilation of a class library and an application that uses that library with the following command-line invocations: <pre class="code-example">
csc /target:library HelloLibrary.cs   
csc /reference:HelloLibrary.dll HelloApp.cs  
</pre>which produce a class library named HelloLibrary.dll and an application named HelloApp.exe. </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>
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