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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="20.4.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="20.4.2.htm"><img src="next.gif" alt="next" border="0" /></a></span><span class="clause-depth"><a href="19.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="21.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="20.htm">20</a></span><span class="clause-title-previous"> Interfaces</span></span><span class="clause-depth"><a href="20.3.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="20.4.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="20.4.htm">20.4</a></span><span class="clause-title-previous"> Interface implementations</span></span><span class="clause-depth"><a href="20.4.1.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="20.4.2.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">20.4.1</span><span class="clause-title"> Explicit interface member implementations</span></span><span class="locator">
     Paragraph 1</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P1S1"></a>For purposes of implementing interfaces, a class or struct may declare explicit interface member implementations.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P1S2"></a>An explicit interface member implementation is a method, property, event, or indexer declaration that references a fully qualified interface member name.</span> <span class="example">[Example: For example <pre class="code-example">
interface ICloneable  
{  
   object Clone();  
}  
interface IComparable  
{  
   int CompareTo(object other);  
}  
class ListEntry: ICloneable, IComparable  
{  
   object ICloneable.Clone() {...}  
   int IComparable.CompareTo(object other) {...}  
}  
</pre></span></span><span class="paragraph"><span class="example">Here, ICloneable.Clone and IComparable.CompareTo are explicit interface member implementations. end example]</span> </span><span class="paragraph"><span class="example">[Example: In some cases, the name of an interface member may not be appropriate for the implementing class, in which case the interface member may be implemented using explicit interface member implementation. A class implementing a file abstraction, for example, would likely implement a Close member function that has the effect of releasing the file resource, and implement the Dispose method of the IDisposable interface using explicit interface member implementation: <pre class="code-example">
interface IDisposable {  
   void Dispose();  
}  
class MyFile: IDisposable {  
   void IDisposable.Dispose() {  
      Close();  
   }  
   public void Close() {  
      // Do what's necessary to close the file  
      System.GC.SuppressFinalize(this);  
   }  
}  
</pre>end example]</span> </span><span class="locator">
     Paragraph 2</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P2S1"></a>It is not possible to access an explicit interface member implementation through its fully qualified name in a method invocation, property access, or indexer access.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P2S2"></a>An explicit interface member implementation can only be accessed through an interface instance, and is in that case referenced simply by its member name.</span> </span><span class="locator">
     Paragraph 3</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P3S1"></a>It is a compile-time error for an explicit interface member implementation to include access modifiers, and it is a compile-time error to include the modifiers abstract, virtual, override, or static.</span> </span><span class="locator">
     Paragraph 4</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P4S1"></a>Explicit interface member implementations have different accessibility characteristics than other members.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P4S2"></a>Because explicit interface member implementations are never accessible through their fully qualified name in a method invocation or a property access, they are in a sense private.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P4S3"></a>However, since they can be accessed through an interface instance, they are in a sense also public.</span> </span><span class="locator">
     Paragraph 5</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P5S1"></a>Explicit interface member implementations serve two primary purposes: </span><ul><li><span class="sentence"><span class="sentence-number">2</span> <a name="P5S2"></a> Because explicit interface member implementations are not accessible through class or struct instances, they allow interface implementations to be excluded from the public interface of a class or struct.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P5S3"></a>This is particularly useful when a class or struct implements an internal interface that is of no interest to a consumer of that class or struct.</span> </li><li><span class="sentence"><span class="sentence-number">4</span> <a name="P5S4"></a> Explicit interface member implementations allow disambiguation of interface members with the same signature.</span> <span class="sentence"><span class="sentence-number">5</span> <a name="P5S5"></a>Without explicit interface member implementations it would be impossible for a class or struct to have different implementations of interface members with the same signature and return type, as would it be impossible for a class or struct to have any implementation at all of interface members with the same signature but with different return types.</span> </li></ul></span><span class="locator">
     Paragraph 6</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P6S1"></a>For an explicit interface member implementation to be valid, the class or struct must name an interface in its base class list that contains a member whose fully qualified name, type, and parameter types exactly match those of the explicit interface member implementation.</span> <span class="example">[Example: Thus, in the following class <pre class="code-example">
class Shape: ICloneable  
{  
   object ICloneable.Clone() {...}  
   int IComparable.CompareTo(object other) {...}  // invalid  
}  
</pre>the declaration of IComparable.CompareTo results in a compile-time error because IComparable is not listed in the base class list of Shape and is not a base interface of ICloneable. Likewise, in the declarations <pre class="code-example">
class Shape: ICloneable  
{  
   object ICloneable.Clone() {...}  
}  
class Ellipse: Shape  
{  
   object ICloneable.Clone() {...} // invalid  
}  
</pre>the declaration of ICloneable.Clone in Ellipse results in a compile-time error because ICloneable is not explicitly listed in the base class list of Ellipse. end example]</span> </span><span class="locator">
     Paragraph 7</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P7S1"></a>The fully qualified name of an interface member must reference the interface in which the member was declared.</span> <span class="example">[Example: Thus, in the declarations <pre class="code-example">
interface IControl  
{  
   void Paint();  
}  
interface ITextBox: IControl  
{  
   void SetText(string text);  
}  
class TextBox: ITextBox  
{  
   void IControl.Paint() {...}  
   void ITextBox.SetText(string text) {...}  
}  
</pre>the explicit interface member implementation of Paint must be written as IControl.Paint. end example]</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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