[Nice-commit] Nice/web manual.xml,1.39,1.40

[Francis B. <fb...@us...>]

Update of /cvsroot/nice/Nice/web
In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv10377/web

Modified Files:
	manual.xml 
Log Message:
Added a section explaining the absence of class casting in Nice.


Index: manual.xml
===================================================================
RCS file: /cvsroot/nice/Nice/web/manual.xml,v
retrieving revision 1.39
retrieving revision 1.40
diff -C2 -d -r1.39 -r1.40
*** manual.xml	2 Sep 2004 16:48:58 -0000	1.39
--- manual.xml	16 Sep 2004 14:21:27 -0000	1.40
***************
*** 16,19 ****
--- 16,20 ----
      <author><firstname>Daniel</firstname><surname>Bonniot</surname></author>
      <author><firstname>Bryn</firstname><surname>Keller</surname></author>
+     <author><firstname>Francis></firstname><surname>Barber</surname></author>
      <copyright><year>2003</year><holder>Daniel Bonniot</holder></copyright>
    </bookinfo>
***************
*** 1950,1953 ****
--- 1951,1991 ----
        </para>
        </section>
+       
+       <section id="classCasting"><title>Class Casting</title>
+         <para>
+         Class casting is not used in Nice.  Similar to <link 
+         linkend="optionTypes">Option types</link> and nullness, if the compiler
+         can prove that the type of an object is compatible with the target
+         context, it will allow that object to be used.  This can be done using
+         the <literal>instanceof</literal> operator and an <literal>if</literal>
+         statement:
+         </para>
+ <example>
+   <title>Title</title>
+ <programlisting lang="nice">
+ 	void foo(FileOutputStream arg) {...}
+ 	
+ 	void bar(OutputStream arg) {
+ 		if (arg instanceof FileOutputStream) {
+ 			//Here Nice knows arg is a FileOutputStream, so it can 
+ 			// be passed to a method which takes a FileOutputStream.
+ 			foo(arg);
+ 		} 
+ 		foo(arg); //Here arg may or may not be a FileOutputStream, 
+ 			  //so Nice gives a compilation error.
+ 	}
+ </programlisting>
+ </example>
+         <para>
+         As with <link linkend="optionTypes">Option types</link>, type inference
+         doesn't work on fields of objects or on method calls, only on local
+         variables. There's a good reason for this: the value of an instance 
+         variable may have changed (updated by another thread, perhaps) between
+         the time the value was checked for its type and the time it is actually
+         used. Similarly, method calls can return objects of different sub-types
+         every time they are called.  To avoid this problem, simply assign the
+         value to a local variable first.
+         </para>
+       </section>
  
        <section id = "typeParameters"><title>Type Parameters</title>
***************
*** 2199,2201 ****
    sgml-validate-command: "xmllint -noout -valid"
    End:
!  -->
--- 2237,2239 ----
    sgml-validate-command: "xmllint -noout -valid"
    End:
!  -->
\ No newline at end of file