Extend switch .. case statement for Object types and simple expressions

[Ulf Zibis]

Another advanced example to minimize chance for NPE:

    switch( .equals(myString)) { // alternative: ?.equals(myString)
        case "foo" : foo(); break;
        case "bar" : bar(); break;
        default : dontCare();
    }



Am 30.03.2009 20:31, Ulf Zibis schrieb:
> AUTHOR(S): Ulf Zibis, Cologne, Germany
>
> OVERVIEW
> FEATURE SUMMARY: Extend switch .. case statement for Object types and simple expressions.
> MAJOR ADVANTAGE:
> - Increases readability of source in concurrence to if .. else if .. else syntax.
> - Sophisticated jumps.
> MAJOR BENEFIT:
> Stop some programmers escaping to some modern scripting language.
> MAJOR DISADVANTAGE:
> Programmers from other languages, especially C, may be confused about such rich syntax.
>
> EXAMPLES
> SIMPLE EXAMPLE:
> (1):
>     switch( myObject) {
>         case CONSTANT1 : doSomething(); break;
>         case CONSTANT2 : doSomethingElse(); break;
>         default : doSomethingDefault();
>     }
> (2):
>     switch( myString) {
>         case equals("red") : stop(); break;
>         case equals("green") : go(); break;
>         default : openYourEyesForCrossingTraffic();
>     }
> (3):
>     switch( myString) {
>         case equalsIgnoreCase("RED") : sureStop(); break;
>         case equalsIgnoreCase("GREEN") : sureGo(); break;
>         default : beAwareOfPoliceWachtingYou();
>     }
>
> ADVANCED EXAMPLE:
> (1):
>     switch( primitiveInt) {
>         case == 10 : doOnlyIf10(); // alternative syntax for 'case 10:'
>         case < 10 :
>         case >= 20 : break;
>         default : doOnlyInRange();
>     }
> (2):
>     switch( primitiveInt) {
>         case (>= 10 && < 20) : doOnlyInRange();
>         default : throw new Exception("Out of range");
>     }
> (3):
>     switch( myString) {
>         case contains("foo") : doSomething(); break;
>         case regionMatches(true, 2, otherString, 4, 6) : doSomethingElse(); break;
>         default : doSomethingDefault();
>     }
> (4):
>     switch( myString.equals()) { // alternative: myString.equals(..)
>         case "foo" : foo(); break;
>         case "bar" : bar(); break;
>         default : dontCare();
>     }
> (5):
>     switch( className.startsWith("String", ..)) { // alternative: className.startsWith("String", ?)
>         case 0 : doForSimpleName(); break;
>         case 9 : doForFullName(); break;
>         default : canNotDecide();
>     }
> (6):
>     switch( anyObjectOrPrimitive instanceof) { // note, that casting is solved implicit
>         case boolean, byte, ... float : break; // Don't do anything
>         case double : forDouble(anyObjectOrPrimitive);
>         case HashMap :
>         case TreeMap : forPlattformMap(anyObjectOrPrimitive); break;
>         case Map : forOtherMap(anyObjectOrPrimitive); break;
>         default : forObject(anyObjectOrPrimitive);
>     }
> (7):
>     switch( some_lethargic_function_we_cant_call_much().equals(..) ) {
>         case "this":
>         case "that":       this_or_that(); break;
>         case "bigjump":    big();    // fall
>         case "jump":       jump(); break;
>         case "secondlastchance":
>         case "lastchance": last_chance(); break;
>         default:           do_default();
>     }
> .. as replacement for:
>     String sSomeString = some_lethargic_function_we_cant_call_much();
>     if( sSomeString.equals( "this" ) || sSomeString.equals( "that" ) )
>         this_or_that();
>     else if( sSomeString.equals( "jump" ) || sSomeString.equals( "bigjump" ) )
>     {
>         if( sSomeString.equals( "bigjump" ) )
>             big();
>         jump();
>     } else if( sSomeString.equals( "secondlastchance" ) ||
>             sSomeString.equals( "lastchance" ) )
>     {
>         last_chance();
>     } else do_default();
>
> ALTERNATIVES:
>     switch( myString) {  // note the '.', I personally would prefer this alternative!
>         case .equals("red") : stop(); break;
>         case .equals("green") : go(); break;
>         default : openYourEyesForCrossingTraffic();
>     }
>     switch( primitiveInt) {  // note the '.'
>         case (. >= 10 && . < 20) : doOnlyInRange();
> //        case (? >= 10 && ? < 20) : doOnlyInRange(); // alternative
>         default : throw new Exception("Out of range");
>     }
>
>
> DETAILS
> SPECIFICATION:
> The new syntax should be interpreted as
>     switch ( leftExpressionPart ) {
>         case rightExpressionPart1 :
>         case rightExpressionPart2 :
>         ...
>         default :
>     }
> The result of entire expression should be boolean type.
> There is shortcut for:
>     leftExpressionPart: intVariable
>     rightExpressionPart: == intLiteral
> (the '==' could be ommitted.)
>
> COMPILATION:
> Compiler could first pre-compile to appropriate if..then..else syntax.
> Bytecode would not be affected, but in special cases it could be more compact, if noted pre-compilation would be replaced by sophisticated optimization.
> TESTING:
> Compiler byte-code results for new syntax should be same than from equivalent hand-coded legacy if..then..else syntax
> . Exception: sophisticated optimization.
> LIBRARY SUPPORT: No supporting libraries are needed for the feature?
> REFLECTIVE APIS: There should not be any affection to reflection API.
> OTHER CHANGES: No.
> MIGRATION:
> No refactoring is needed to stay compatible.
>
> COMPATIBILITY
> BREAKING CHANGES:
> No previously valid programs are now invalid.
> ... but ATTENTION:
> If proposals from some other guys regarding "Strings in switch" would be taken into JDK 7, there won't be any compatible way to implement my more general proposal in future version of JDK !!!
> --> So switch .. case statement should compare for IDENTITY if not syntactically determined otherwise.
> --> compare for EQUALITY would also break semantic of existing switch .. case statement.
> EXISTING PROGRAMS:
> Source and class files of earlier platform versions interact with the feature without any notice.
>
> REFERENCES
> http://mail.openjdk.java.net/pipermail/coin-dev/2009-February/000001.html
> http://mail.openjdk.java.net/pipermail/coin-dev/2009-March/000213.html
> http://mail.openjdk.java.net/pipermail/coin-dev/2009-March/000855.html
> http://forums.java.net/jive/thread.jspa?messageID=27781&#27781
> http://forums.java.net/jive/thread.jspa?messageID=15769&#15769
> http://forums.java.net/jive/thread.jspa?messageID=27773&#27773
> http://forums.java.net/jive/thread.jspa?messageID=11393&#11393
> EXISTING BUGS:
> http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=5012262
> URL FOR PROTOTYPE (optional):
>
>
>
>
>