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Subject: Conversions: Implicit and Explicit - C# Nuts and Bolt - Beta2
Date: Wed, 29 Aug 2007 13:28:45 +0800
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<DIV class=3DSection1>
<P class=3DMsoNormal><IMG id=3D_x0000_i1025 height=3D48=20
src=3D"http://www.vijaymukhi.com/documents/books/csadv/bpb.jpg" =
width=3D64></P>
<P class=3DMsoNormal><![if =
!supportEmptyParas]><![endif]>&nbsp;<o:p></o:p></P>
<P class=3DMsoNormal><SPAN=20
style=3D"FONT-SIZE: 15pt; COLOR: black; FONT-FAMILY: Garamond">Chapter=20
6</SPAN></P>
<P class=3DMsoNormal><![if =
!supportEmptyParas]><![endif]>&nbsp;<o:p></o:p></P>
<P class=3DMsoNormal style=3D"mso-layout-grid-align: none"><SPAN=20
style=3D"FONT-SIZE: 26pt; COLOR: black; FONT-FAMILY: =
Garamond">Conversions:=20
</SPAN><SPAN style=3D"FONT-SIZE: 26pt; FONT-FAMILY: Garamond">Implicit =
and=20
Explicit</SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]>&nbsp;<o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext">Most of us imply all =
the time and=20
are rarely explicit. <o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]>&nbsp;<o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext">The C# programming =
language has=20
exactly 78 keywords in all. But there are only two types of conversions, =

implicit and explicit. As the name suggest, an explicit conversion has =
to be=20
specifically supplied by using a cast and at all other times, the =
conversion is=20
considered to be implicit.<SPAN style=3D"mso-spacerun: yes">&nbsp;=20
</SPAN>Conversion comes into play when converting from a source type to =
a target=20
type, which is finally the return value of the operator. =
<o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]>&nbsp;<o:p></o:p></SPAN></P>
<P class=3DCprg><U>a.cs</U><o:p></o:p></P>
<P class=3DCprg>public class zzz <o:p></o:p></P>
<P class=3DCprg>{<o:p></o:p></P>
<P class=3DCprg>public static void Main()<o:p></o:p></P>
<P class=3DCprg>{<o:p></o:p></P>
<P class=3DCprg>yyy a =3D new yyy();<o:p></o:p></P>
<P class=3DCprg>yyy b =3D new yyy();<o:p></o:p></P>
<P class=3DCprg>System.Console.WriteLine(a+b);<o:p></o:p></P>
<P class=3DCprg>}<o:p></o:p></P>
<P class=3DCprg>}<o:p></o:p></P>
<P class=3DCprg>class yyy<SPAN style=3D"mso-spacerun: yes">&nbsp;=20
</SPAN><o:p></o:p></P>
<P class=3DCprg>{<o:p></o:p></P>
<P class=3DCprg>public implicit operator xxx (int b)<o:p></o:p></P>
<P class=3DCprg>{<o:p></o:p></P>
<P class=3DCprg>return new xxx();<o:p></o:p></P>
<P class=3DCprg>} <o:p></o:p></P>
<P class=3DCprg>}<o:p></o:p></P>
<P class=3DCprg>class xxx<o:p></o:p></P>
<P class=3DCprg>{<o:p></o:p></P>
<P class=3DCprg>}<o:p></o:p></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]>&nbsp;<o:p></o:p></SPAN></P>
<P class=3DCoutput><U>Compiler Error</U><o:p></o:p></P>
<P class=3DCoutput>a.cs(12,8): error CS0556: User-defined conversion =
must convert=20
to or from the enclosing type<o:p></o:p></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]>&nbsp;<o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext">The rules for =
user-defined=20
conversions are extremely simple. They have to accept one parameter, =
similar to=20
unary operators, and must be of the same data type as of the class. =
Under normal=20
circumstances, conversion operators do not have a return type as it =
assumes the=20
return type to be that of the operator type. The return data type should =

directly or indirectly be the data type that is being enclosed within =
the=20
brackets. <o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]>&nbsp;<o:p></o:p></SPAN></P>
<P class=3DCprg><U>a.cs</U><o:p></o:p></P>
<P class=3DCprg>public class zzz <o:p></o:p></P>
<P class=3DCprg>{<o:p></o:p></P>
<P class=3DCprg>public static void Main()<o:p></o:p></P>
<P class=3DCprg>{<o:p></o:p></P>
<P class=3DCprg>yyy a =3D new yyy();<o:p></o:p></P>
<P class=3DCprg>yyy b =3D new yyy();<o:p></o:p></P>
<P class=3DCprg>}<o:p></o:p></P>
<P class=3DCprg>}<o:p></o:p></P>
<P class=3DCprg>class yyy<SPAN style=3D"mso-spacerun: yes">&nbsp;=20
</SPAN><o:p></o:p></P>
<P class=3DCprg>{<o:p></o:p></P>
<P class=3DCprg>public static implicit operator xxx (yyy =
b)<o:p></o:p></P>
<P class=3DCprg>{<o:p></o:p></P>
<P class=3DCprg>return new yyy();<o:p></o:p></P>
<P class=3DCprg>} <o:p></o:p></P>
<P class=3DCprg>}<o:p></o:p></P>
<P class=3DCprg>class xxx<o:p></o:p></P>
<P class=3DCprg>{<o:p></o:p></P>
<P class=3DCprg>}<o:p></o:p></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]>&nbsp;<o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext">At times, we can =
catch the=20
compiler napping. We are returning a yyy object and not an xxx. As per =
the=20
compiler rules, we should have received an error as we are to return an =
xxx,=20
whereas we are returning a yyy object. May be, as all classes are =
derived from=20
object, so the compiler either misses the error or condones=20
it.<o:p></o:p></SPAN></P>
<P class=3DCbase><SPAN style=3D"COLOR: windowtext"><![if =
!supportEmptyParas]><![endif]>&nbsp;<o:p></o:p></SPAN></P>
<P class=3DCprg><U>a.cs</U><o:p></o:p></P>
<P class=3DCprg>public class zzz <o:p></o:p></P>
<P class=3DCprg>{<o:p></o:p></P>
<P class=3DCprg>public static void Main()<o:p></o:p></P>
<P class=3DCprg>{<o:p></o:p></P>
<P class=3DCprg>yyy a =3D new yyy();<o:p></o:p></P>
<P class=3DCprg>yyy b =3D new yyy();<o:p></o:p></P>
<P class=3DCprg>}<o:p></o:p></P>
<P class=3DCprg>}<o:p></o:p></P>
<P class=3DCprg>class yyy<SPAN style=3D"mso-spacerun: yes">&nbsp;=20
</SPAN><o:p></o:p></P>
<P class=3DCprg>{<o:p></o:p></P>
<P class=3DCprg>public static implicit operator xxx (yyy =
b)<o:p></o:p></P>
<P class=3DCprg>{<o:p></o:p></P>
<P class=3DCprg>return new aaa();<o:p></o:p></P>
<P class=3DCprg>} <o:p></o:p></P>
<P class=3DCprg>}<o:p></o:p></P>
<P class=3DCprg>class xxx<o:p></o:p></P>
<P class=3DCprg>{<o:p></o:p></P>
<P class=3DCprg>}<o:p></o:p></P>
<P class=3DCprg>class aaa<o:p></o:p></P>
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