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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="17.11.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="18.htm"><img src="next.gif" alt="next" border="0" /></a></span><span class="clause-depth"><a href="16.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="18.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="17.htm">17</a></span><span class="clause-title-previous"> Classes</span></span><span class="clause-depth"><a href="17.11.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="17.12.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">17.12</span><span class="clause-title"> Destructors</span></span><span class="locator">
Paragraph 1</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P1S1"></a>A destructor is a member that implements the actions required to destruct an instance of a class.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P1S2"></a>A destructor is declared using a destructor-declaration: <span class="grammar-production"><span class="name"><a name="destructor-declaration"></a>destructor-declaration</span> : <span class="rhs"><span class="non-terminal"><a href="24.2.htm#attributes">attributes</a></span><sub>opt</sub> <span class="keyword">extern</span><sub>opt</sub> <span class="terminal">~</span> <span class="non-terminal"><a href="9.4.2.htm#identifier">identifier</a></span> <span class="terminal">(</span> <span class="terminal">)</span> <span class="non-terminal"><a href="17.12.htm#destructor-body">destructor-body</a></span> </span></span><span class="grammar-production"><span class="name"><a name="destructor-body"></a>destructor-body</span> : <span class="rhs"><span class="non-terminal"><a href="15.2.htm#block">block</a></span> </span><span class="rhs"><span class="terminal">;</span> </span></span></span></span><span class="locator">
Paragraph 2</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P2S1"></a>A <span class="non-terminal"><a href="17.12.htm#destructor-declaration">destructor-declaration</a></span> may include a set of attributes (<a href="24.htm">§24</a>).</span> </span><span class="locator">
Paragraph 3</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P3S1"></a>The identifier of a destructor-declarator must name the class in which the destructor is declared.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P3S2"></a>If any other name is specified, a compile-time error occurs.</span> </span><span class="locator">
Paragraph 4</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P4S1"></a>When a destructor declaration includes an extern modifier, the destructor is said to be an external destructor.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P4S2"></a>Because an external destructor declaration provides no actual implementation, its <span class="non-terminal"><a href="17.12.htm#destructor-body">destructor-body</a></span> consists of a semicolon.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P4S3"></a>For all other destructors, the <span class="non-terminal"><a href="17.12.htm#destructor-body">destructor-body</a></span> consists of a block, which specifies the statements to execute in order to destruct an instance of the class.</span> <span class="sentence"><span class="sentence-number">4</span> <a name="P4S4"></a>A <span class="non-terminal"><a href="17.12.htm#destructor-body">destructor-body</a></span> corresponds exactly to the <span class="non-terminal"><a href="17.5.htm#method-body">method-body</a></span> of an instance method with a <span class="keyword">void</span> return type (<a href="17.5.8.htm">§17.5.8</a>).</span> </span><span class="locator">
Paragraph 5</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P5S1"></a>Destructors are not inherited.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P5S2"></a>Thus, a class has no destructors other than the one which may be declared in that class.</span> </span><span class="paragraph"><span class="note">[Note: Since a destructor is required to have no parameters, it cannot be overloaded, so a class can have, at most, one destructor. end note]</span> </span><span class="locator">
Paragraph 6</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P6S1"></a>Destructors are invoked automatically, and cannot be invoked explicitly.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P6S2"></a>An instance becomes eligible for destruction when it is no longer possible for any code to use that instance.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P6S3"></a>Execution of the destructor for the instance may occur at any time after the instance becomes eligible for destruction.</span> <span class="sentence"><span class="sentence-number">4</span> <a name="P6S4"></a>When an instance is destructed, the destructors in that instance's inheritance chain are called, in order, from most derived to least derived </span><span class="example">[Example: The output of the example <pre class="code-example">
using System;
class A
{
~A() {
Console.WriteLine("A's destructor");
}
}
class B: A
{
~B() {
Console.WriteLine("B's destructor");
}
}
class Test
{
static void Main() {
B b = new B();
b = null;
GC.Collect();
GC.WaitForPendingFinalizers();
}
}
</pre>is <pre class="code-example">
B's destructor
A's destructor
</pre>since destructors in an inheritance chain are called in order, from most derived to least derived. end example]</span> </span><span class="paragraph"><span class="sentence"><span class="sentence-number">5</span> <a name="P6S5"></a>Destructors may be implemented by overriding the virtual method Finalize on System.Object.</span> <span class="sentence"><span class="sentence-number">6</span> <a name="P6S6"></a>In any event, C# programs are not permitted to override this method or call it (or overrides of it) directly.</span> </span><span class="paragraph"><span class="example">[Example: For instance, the program <pre class="code-example">
class A
{
override protected void Finalize() {} // error
public void F() {
this.Finalize(); // error
}
}
</pre>contains two errors. end example]</span> </span><span class="paragraph"><span class="sentence"><span class="sentence-number">7</span> <a name="P6S7"></a>The compiler behaves as if this method, and overrides of it, does not exist at all.</span> <span class="example">[Example: Thus, this program: <pre class="code-example">
class A
{
void Finalize() {} // permitted
}
</pre>is valid and the method shown hides System.Object's Finalize method. end example]</span> </span><span class="paragraph"><span class="sentence"><span class="sentence-number">8</span> <a name="P6S8"></a>For a discussion of the behavior when an exception is thrown from a destructor, see <a href="23.3.htm">§23.3</a>.</span> <span class="table-line"></span>
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