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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="14.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="14.1.1.htm"><img src="next.gif" alt="next" border="0" /></a></span><span class="clause-depth"><a href="13.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="15.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="14.htm">14</a></span><span class="clause-title-previous"> Expressions</span></span><span class="clause-depth"><a href="14.1.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="14.2.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">14.1</span><span class="clause-title"> Expression classifications</span></span><span class="locator">
Paragraph 1</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P1S1"></a>An expression is classified as one of the following: </span><ul><li><span class="sentence"><span class="sentence-number">2</span> <a name="P1S2"></a> A value.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P1S3"></a>Every value has an associated type.</span> </li><li><span class="sentence"><span class="sentence-number">4</span> <a name="P1S4"></a> A variable.</span> <span class="sentence"><span class="sentence-number">5</span> <a name="P1S5"></a>Every variable has an associated type, namely the declared type of the variable.</span> </li><li><span class="sentence"><span class="sentence-number">6</span> <a name="P1S6"></a> A namespace.</span> <span class="sentence"><span class="sentence-number">7</span> <a name="P1S7"></a>An expression with this classification can only appear as the left-hand side of a <span class="non-terminal"><a href="14.5.4.htm#member-access">member-access</a></span> (<a href="14.5.4.htm">§14.5.4</a>).</span> <span class="sentence"><span class="sentence-number">8</span> <a name="P1S8"></a>In any other context, an expression classified as a namespace causes a compile-time error.</span> </li><li><span class="sentence"><span class="sentence-number">9</span> <a name="P1S9"></a> A type.</span> <span class="sentence"><span class="sentence-number">10</span> <a name="P1S10"></a>An expression with this classification can only appear as the left-hand side of a <span class="non-terminal"><a href="14.5.4.htm#member-access">member-access</a></span> (<a href="14.5.4.htm">§14.5.4</a>), or as an operand for the as operator (<a href="14.9.10.htm">§14.9.10</a>), the is operator (<a href="14.9.9.htm">§14.9.9</a>), or the typeof operator (<a href="14.5.11.htm">§14.5.11</a>).</span> <span class="sentence"><span class="sentence-number">11</span> <a name="P1S11"></a>In any other context, an expression classified as a type causes a compile-time error.</span> </li><li><span class="sentence"><span class="sentence-number">12</span> <a name="P1S12"></a> A method group, which is a set of overloaded methods resulting from a member lookup (<a href="14.3.htm">§14.3</a>).</span> <span class="sentence"><span class="sentence-number">13</span> <a name="P1S13"></a>A method group may have an associated instance expression.</span> <span class="sentence"><span class="sentence-number">14</span> <a name="P1S14"></a>When an instance method is invoked, the result of evaluating the instance expression becomes the instance represented by this (<a href="14.5.7.htm">§14.5.7</a>).</span> <span class="sentence"><span class="sentence-number">15</span> <a name="P1S15"></a>A method group is only permitted in an <span class="non-terminal"><a href="14.5.5.htm#invocation-expression">invocation-expression</a></span> (<a href="14.5.5.htm">§14.5.5</a>) or a <span class="non-terminal"><a href="14.5.10.3.htm#delegate-creation-expression">delegate-creation-expression</a></span> (<a href="14.5.10.3.htm">§14.5.10.3</a>).</span> <span class="sentence"><span class="sentence-number">16</span> <a name="P1S16"></a>In any other context, an expression classified as a method group causes a compile-time error.</span> </li><li><span class="sentence"><span class="sentence-number">17</span> <a name="P1S17"></a> A property access.</span> <span class="sentence"><span class="sentence-number">18</span> <a name="P1S18"></a>Every property access has an associated type, namely the type of the property.</span> <span class="sentence"><span class="sentence-number">19</span> <a name="P1S19"></a>Furthermore, a property access may have an associated instance expression.</span> <span class="sentence"><span class="sentence-number">20</span> <a name="P1S20"></a>When an accessor (the get or set block) of an instance property access is invoked, the result of evaluating the instance expression becomes the instance represented by this (<a href="14.5.7.htm">§14.5.7</a>).</span> </li><li><span class="sentence"><span class="sentence-number">21</span> <a name="P1S21"></a> An event access.</span> <span class="sentence"><span class="sentence-number">22</span> <a name="P1S22"></a>Every event access has an associated type, namely the type of the event.</span> <span class="sentence"><span class="sentence-number">23</span> <a name="P1S23"></a>Furthermore, an event access may have an associated instance expression.</span> <span class="sentence"><span class="sentence-number">24</span> <a name="P1S24"></a>An event access may appear as the left-hand operand of the += and -= operators (<a href="14.13.3.htm">§14.13.3</a>).</span> <span class="sentence"><span class="sentence-number">25</span> <a name="P1S25"></a>In any other context, an expression classified as an event access causes a compile-time error.</span> </li><li><span class="sentence"><span class="sentence-number">26</span> <a name="P1S26"></a> An indexer access.</span> <span class="sentence"><span class="sentence-number">27</span> <a name="P1S27"></a>Every indexer access has an associated type, namely the element type of the indexer.</span> <span class="sentence"><span class="sentence-number">28</span> <a name="P1S28"></a>Furthermore, an indexer access has an associated instance expression and an associated argument list.</span> <span class="sentence"><span class="sentence-number">29</span> <a name="P1S29"></a>When an accessor (the get or set block) of an indexer access is invoked, the result of evaluating the instance expression becomes the instance represented by this (<a href="14.5.7.htm">§14.5.7</a>), and the result of evaluating the argument list becomes the parameter list of the invocation.</span> </li><li><span class="sentence"><span class="sentence-number">30</span> <a name="P1S30"></a> Nothing.</span> <span class="sentence"><span class="sentence-number">31</span> <a name="P1S31"></a>This occurs when the expression is an invocation of a method with a return type of <span class="keyword">void</span>.</span> <span class="sentence"><span class="sentence-number">32</span> <a name="P1S32"></a>An expression classified as nothing is only valid in the context of a <span class="non-terminal"><a href="15.6.htm#statement-expression">statement-expression</a></span> (<a href="15.6.htm">§15.6</a>).</span> </li></ul></span><span class="locator">
Paragraph 2</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P2S1"></a>The final result of an expression is never a namespace, type, method group, or event access.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P2S2"></a>Rather, as noted above, these categories of expressions are intermediate constructs that are only permitted in certain contexts.</span> </span><span class="locator">
Paragraph 3</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P3S1"></a>A property access or indexer access is always reclassified as a value by performing an invocation of the get-accessor or the set-accessor.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P3S2"></a>The particular accessor is determined by the context of the property or indexer access: If the access is the target of an assignment, the set-accessor is invoked to assign a new value (<a href="14.13.1.htm">§14.13.1</a>).</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P3S3"></a>Otherwise, the get-accessor is invoked to obtain the current value (<a href="14.1.1.htm">§14.1.1</a>).</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>⌨️ 快捷键说明
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