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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="14.2.1.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="14.2.3.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="14.3.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="14.2.htm">14.2</a></span><span class="clause-title-previous"> Operators</span></span><span class="clause-depth"><a href="14.2.1.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="14.2.3.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">14.2.2</span><span class="clause-title"> Operator overloading</span></span><span class="locator">
Paragraph 1</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P1S1"></a>All unary and binary operators have predefined implementations that are automatically available in any expression.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P1S2"></a>In addition to the predefined implementations, user-defined implementations can be introduced by including operator declarations in classes and structs (<a href="17.9.htm">§17.9</a>).</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P1S3"></a>User-defined operator implementations always take precedence over predefined operator implementations: Only when no applicable user-defined operator implementations exist will the predefined operator implementations be considered.</span> </span><span class="locator">
Paragraph 2</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P2S1"></a>The overloadable unary operators are: <pre class="code-example">
+ - ! ~ ++ -- true false
</pre></span></span><span class="paragraph"><span class="note">[Note: Although true and false are not used explicitly in expressions, they are considered operators because they are invoked in several expression contexts: boolean expressions (<a href="14.16.htm">§14.16</a>) and expressions involving the conditional (<a href="14.12.htm">§14.12</a>), and conditional logical operators (<a href="14.11.htm">§14.11</a>). end note]</span> </span><span class="paragraph"><span class="sentence"><span class="sentence-number">2</span> <a name="P2S2"></a>The overloadable binary operators are: <pre class="code-example">
+ - * / % & | ^ << >> == != > < >= <=
</pre></span></span><span class="locator">
Paragraph 3</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P3S1"></a>Only the operators listed above can be overloaded.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P3S2"></a>In particular, it is not possible to overload member access, method invocation, or the =, &&, ||, ?:, checked, unchecked, new, typeof, as, and is operators.</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 binary operator is overloaded, the corresponding assignment operator, if any, is also implicitly overloaded.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P4S2"></a>For example, an overload of operator * is also an overload of operator *=.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P4S3"></a>This is described further in <a href="14.13.htm">§14.13</a>.</span> <span class="sentence"><span class="sentence-number">4</span> <a name="P4S4"></a>Note that the assignment operator itself (=) cannot be overloaded.</span> <span class="sentence"><span class="sentence-number">5</span> <a name="P4S5"></a>An assignment always performs a simple bit-wise copy of a value into a variable.</span> </span><span class="locator">
Paragraph 5</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P5S1"></a>Cast operations, such as (T)x, are overloaded by providing user-defined conversions (<a href="13.4.htm">§13.4</a>).</span> </span><span class="locator">
Paragraph 6</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P6S1"></a>Element access, such as a[x], is not considered an overloadable operator.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P6S2"></a>Instead, user-defined indexing is supported through indexers (<a href="17.8.htm">§17.8</a>).</span> </span><span class="locator">
Paragraph 7</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P7S1"></a>In expressions, operators are referenced using operator notation, and in declarations, operators are referenced using functional notation.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P7S2"></a>The following table shows the relationship between operator and functional notations for unary and binary operators.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P7S3"></a>In the first entry, op denotes any overloadable unary prefix operator.</span> <span class="sentence"><span class="sentence-number">4</span> <a name="P7S4"></a>In the second entry, op denotes the unary postfix ++ and --operators.</span> <span class="sentence"><span class="sentence-number">5</span> <a name="P7S5"></a>In the third entry, op denotes any overloadable binary operator.</span> <span class="note">[Note: For an example of overloading the ++ and --operators see <a href="17.9.1.htm">§17.9.1</a>. end note]</span>
<table border="1">
<tr>
<td><b>Operator notation</b></td>
<td><b>Functional notation</b></td>
</tr>
<tr>
<td>op x</td>
<td>operator op(x)</td>
</tr>
<tr>
<td>x op</td>
<td>operator op(x)</td>
</tr>
<tr>
<td>x op y</td>
<td>operator op(x,y)</td>
</tr>
</table>
</span><span class="locator">
Paragraph 8</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P8S1"></a>User-defined operator declarations always require at least one of the parameters to be of the class or struct type that contains the operator declaration.</span> <span class="note">[Note: Thus, it is not possible for a user-defined operator to have the same signature as a predefined operator. end note]</span> </span><span class="locator">
Paragraph 9</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P9S1"></a>User-defined operator declarations cannot modify the syntax, precedence, or associativity of an operator.</span> </span><span class="paragraph"><span class="example">[Example: For example, the / operator is always a binary operator, always has the precedence level specified in <a href="14.2.1.htm">§14.2.1</a>, and is always left-associative. end example]</span> </span><span class="paragraph"><span class="note">[Note: While it is possible for a user-defined operator to perform any computation it pleases, implementations that produce results other than those that are intuitively expected are strongly discouraged. </span></span><span class="paragraph"><span class="note">For example, an implementation of operator == should compare the two operands for equality and return an appropriate <span class="keyword">bool</span> result. end note]</span> </span><span class="locator">
Paragraph 10</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P10S1"></a>The descriptions of individual operators in <a href="14.5.htm">§14.5</a> through <a href="14.13.htm">§14.13</a> specify the predefined implementations of the operators and any additional rules that apply to each operator.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P10S2"></a>The descriptions make use of the terms unary operator overload resolution, binary operator overload resolution, and numeric promotion, definitions of which are found in the following sections.</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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