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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="14.11.1.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="14.12.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="14.10.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="14.12.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="14.11.htm">14.11</a></span><span class="clause-title-previous"> Conditional logical operators</span></span><span class="clause-depth"><a href="14.11.1.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="14.11.2.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">14.11.2</span><span class="clause-title"> User-defined conditional logical operators</span></span><span class="locator">
Paragraph 1</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P1S1"></a>When the operands of && or || are of types that declare an applicable user-defined operator & or operator |, both of the following must be true, where T is the type in which the selected operator is declared: </span><ul><li><span class="sentence"><span class="sentence-number">2</span> <a name="P1S2"></a> The return type and the type of each parameter of the selected operator must be T.</span> <span class="sentence"><span class="sentence-number">3</span> <a name="P1S3"></a>In other words, the operator must compute the logical AND or the logical OR of two operands of type T, and must return a result of type T.</span> </li><li><span class="sentence"><span class="sentence-number">4</span> <a name="P1S4"></a> T must contain declarations of operator true and operator false.</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>A compile-time error occurs if either of these requirements is not satisfied.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P2S2"></a>Otherwise, the && or || operation is evaluated by combining the user-defined operator true or operator false with the selected user-defined operator: </span><ul><li><span class="sentence"><span class="sentence-number">3</span> <a name="P2S3"></a> The operation x && y is evaluated as T.false(x) ? x : T.&(x, y), where T.false(x) is an invocation of the operator false declared in T, and T.&(x, y) is an invocation of the selected operator &.</span> <span class="sentence"><span class="sentence-number">4</span> <a name="P2S4"></a>In other words, x is first evaluated and operator false is invoked on the result to determine if x is definitely false.</span> <span class="sentence"><span class="sentence-number">5</span> <a name="P2S5"></a>Then, if x is definitely false, the result of the operation is the value previously computed for x.</span> <span class="sentence"><span class="sentence-number">6</span> <a name="P2S6"></a>Otherwise, y is evaluated, and the selected operator & is invoked on the value previously computed for x and the value computed for y to produce the result of the operation.</span> </li><li><span class="sentence"><span class="sentence-number">7</span> <a name="P2S7"></a> The operation x || y is evaluated as T.true(x) ? x : T.|(x, y), where T.true(x) is an invocation of the operator true declared in T, and T.|(x, y) is an invocation of the selected operator |.</span> <span class="sentence"><span class="sentence-number">8</span> <a name="P2S8"></a>In other words, x is first evaluated and operator true is invoked on the result to determine if x is definitely true.</span> <span class="sentence"><span class="sentence-number">9</span> <a name="P2S9"></a>Then, if x is definitely true, the result of the operation is the value previously computed for x.</span> <span class="sentence"><span class="sentence-number">10</span> <a name="P2S10"></a>Otherwise, y is evaluated, and the selected operator | is invoked on the value previously computed for x and the value computed for y to produce the result of the operation.</span> </li></ul></span><span class="locator">
Paragraph 3</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P3S1"></a>In either of these operations, the expression given by x is only evaluated once, and the expression given by y is either not evaluated or evaluated exactly once.</span> </span><span class="locator">
Paragraph 4</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P4S1"></a>For an example of a type that implements operator true and operator false, see <a href="18.4.2.htm">§18.4.2</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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