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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="11.3.htm"><img src="previous.gif" alt="previous" border="0" /></a><a href="11.3.2.htm"><img src="next.gif" alt="next" border="0" /></a></span><span class="clause-depth"><a href="10.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="12.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="11.htm">11</a></span><span class="clause-title-previous"> Types</span></span><span class="clause-depth"><a href="11.2.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="11.3.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number-link"><a href="11.3.htm">11.3</a></span><span class="clause-title-previous"> Boxing and unboxing</span></span><span class="clause-depth"><a href="11.3.1.htm"><img src="previous.gif" alt="previous at this level" border="0" /></a><a href="11.3.2.htm"><img src="next.gif" alt="next at this level" border="0" /></a> <span class="clause-number">11.3.1</span><span class="clause-title"> Boxing conversions</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 boxing conversion permits any <span class="non-terminal"><a href="11.1.htm#value-type">value-type</a></span> to be implicitly converted to the type object or to any <span class="non-terminal"><a href="11.2.htm#interface-type">interface-type</a></span> implemented by the <span class="non-terminal"><a href="11.1.htm#value-type">value-type</a></span>.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P1S2"></a>Boxing a value of a <span class="non-terminal"><a href="11.1.htm#value-type">value-type</a></span> consists of allocating an object instance and copying the <span class="non-terminal"><a href="11.1.htm#value-type">value-type</a></span> value into that instance.</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 actual process of boxing a value of a <span class="non-terminal"><a href="11.1.htm#value-type">value-type</a></span> is best explained by imagining the existence of a boxing class for that type.</span> <span class="example">[Example: For any <span class="non-terminal"><a href="11.1.htm#value-type">value-type</a></span> T, the boxing class behaves as if it were declared as follows: <pre class="code-example">
sealed class T_Box  
{  
   T value;  
   public T_Box(T t) {  
      value = t;  
   }  
}  
</pre></span></span><span class="paragraph"><span class="example">Boxing of a value v of type T now consists of executing the expression new T_Box(v), and returning the resulting instance as a value of type object. Thus, the statements <pre class="code-example">
int i = 123;  
object box = i;  
</pre>conceptually correspond to <pre class="code-example">
int i = 123;  
object box = new int_Box(i);  
</pre>end example]</span> </span><span class="locator">
     Paragraph 3</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P3S1"></a>Boxing classes like T_Box and int_Box above don't actually exist and the dynamic type of a boxed value isn't actually a class type.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P3S2"></a>Instead, a boxed value of type T has the dynamic type T, and a dynamic type check using the is operator can simply reference type T.</span> <span class="example">[Example: For example, <pre class="code-example">
int i = 123;  
object box = i;  
if (box is int) {  
   Console.Write("Box contains an int");  
}  
</pre>will output the string "Box contains an int" on the console. end example]</span> </span><span class="locator">
     Paragraph 4</span><span class="paragraph"><span class="sentence"><span class="sentence-number">1</span> <a name="P4S1"></a>A boxing conversion implies making a copy of the value being boxed.</span> <span class="sentence"><span class="sentence-number">2</span> <a name="P4S2"></a>This is different from a conversion of a <span class="non-terminal"><a href="11.2.htm#reference-type">reference-type</a></span> to type object, in which the value continues to reference the same instance and simply is regarded as the less derived type object.</span> <span class="example">[Example: For example, given the declaration <pre class="code-example">
struct Point  
{  
   public int x, y;  
   public Point(int x, int y) {  
      this.x = x;  
      this.y = y;  
   }  
}  
</pre>the following statements <pre class="code-example">
Point p = new Point(10, 10);  
object box = p;  
p.x = 20;  
Console.Write(((Point)box).x);  
</pre>will output the value 10 on the console because the implicit boxing operation that occurs in the assignment of p to box causes the value of p to be copied. Had Point been declared a class instead, the value 20 would be output because p and box would reference the same instance. 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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