Personally, I think generics are a waste of time except as a means of
documenting method parameters and return values in library code.
And in cases where want Object anyway, just skip the generics. But that's
just me.
John
On Thu, Aug 14, 2008 at 9:26 AM, Roger Perryman <[EMAIL PROTECTED]>wrote:
> All,
>
> I am converting a project from Xcode 2.x (WO 5.3) to Eclipse 3.4 (WO
> 5.4.2). I have decided to also "upgrade" to using generics. So far, it has
> not been a fun experience. I've read over the threads on this list and
> several of the external references provided. Each time I think I have it
> figured out and try it on my code, I soon discover that I must be missing
> something. In many (but not all) cases, I was able to clear up the errors
> and warnings by making everything <?> or <? extends Object> but it just
> seems wrong to have to explicitly tell it to use whatever it wants. Below
> are a few examples of some typical code snippets that are causing problems.
> What is the correct way to write these using generics?
>
>
> Based on further reading, I know this is not the right way to write this,
> but it works and does not generate errors/warnings.
>
> NSDictionary<Object, Object> tmpDict = new NSDictionary<Object, Object>(
> new NSArray<Object>( new Object[] { location, schedType, Integer.valueOf(
> nWeekday) } ),
> new NSArray<Object>( new Object[] { "toLocation", "toScheduleType",
> "toDay.displayOrder" } ) );
>
> NSArray<?> schedules = EOUtilities.objectsMatchingValues( ec, "Schedule",
> tmpDict );
>
>
> ---------
>
>
> In theory, I believe this is the "more correct" way to write it but this
> generates warnings/errors
>
> NSDictionary<String, ? extends Object> tmpDict = new NSDictionary<String,
> ? extends Object>(
> new NSArray<? extends Object>( new Object[] { location, schedType,
> Integer.valueOf( nWeekday ) } ),
> new NSArray<? extends Object>( new Object[] { "toLocation",
> "toScheduleType", "toDay.displayOrder" } ) );
>
> NSArray<Schedule> schedules = EOUtilities.objectsMatchingValues( ec,
> "Schedule", tmpDict );
>
> One problem with this approach is that, while the keys are, for all intents
> and purposes, Strings, you have to declare the array as <Object> because it
> is created with "new Object[] { entries }."
>
>
> ---------
>
>
> Here, I get a warning icon in the gutter of the first line telling me "The
> expression on type NSArray needs unchecked conversion to conform to
> NSArray<Schedule>." I'm sure this is because EOUtilities don't explicitly
> return an array of Schedules. But, if I change it to <?> or <? extends
> EOGenericRecord> or <? extends EOCustomRecord>, then the warning goes away
> and the next line generates an error icon and complains about the signature
> of showSchedules(). Again, when I alter that, it cascades like dominoes.
>
> NSArray<Schedule> schedules = EOUtilities.objectsForEntityNamed( ec,
> "Schedule" );
> showSchedules( schedules );
>
>
> public static void showSchedules( NSArray<Schedule> schedules );
>
>
> ---------
>
>
> availabilityByPeriods is a dictionary of dictionaries of strings { PERIOD =
> { "HHMM" = "1"; } }
> sKey = "MMDDYYYY_HHMM"
>
> public static NSMutableDictionary<String, ? extends
> Object> arrangeTimeSlotsByPeriod( NSMutableDictionary<String, ? extends
> Object> availabilityByPeriods, String sKey )
> {
> NSMutableDictionary<String, ? extends Object> dateDict =
> newNSMutableDictionary<String, Object>();
> NSMutableDictionary<String, ? extends Object> periodDict =
> newNSMutableDictionary<String, Object>();
> String sDate = sKey.substring( 0, 8 );
> String sTime = sKey.substring( 9 );
> int nPeriod = TimePeriod.timePeriodForKey( sKey );
>
> if ( availabilityByPeriods.objectForKey( sDate ) == null )
> availabilityByPeriods.setObjectForKey( dateDict, sDate );
>
> // Type safety: Unchecked cast from capture#40-of ? extends Object to
> NSMutableDictionary<String, ? extends Object>
> dateDict = (NSMutableDictionary<String, ? extends Object>)
> availabilityByPeriods.objectForKey( sDate );
>
> if ( dateDict.objectForKey( TimePeriod.dayPeriods.objectAtIndex( nPeriod )
> ) == null )
> dateDict.setObjectForKey( periodDict,
> TimePeriod.dayPeriods.objectAtIndex( nPeriod ) );
>
> // Type safety: Unchecked cast from capture#45-of ? extends Object to
> NSMutableDictionary<String, ? extends Object>
> periodDict = (NSMutableDictionary<String, ? extends Object>)
> dateDict.objectForKey( TimePeriod.dayPeriods.objectAtIndex( nPeriod ) );
> periodDict.setObjectForKey( "1", sTime ); // Value is unimportant
> return availabilityByPeriods;
> }
>
> How can I find "capture #x of type expression" as referenced in the error
> messages?
>
>
> ---------
>
>
> This one is even more confusing to me. It looks the same as some of the
> snippets above. Yet, in this case, it complains that "the constructor
> NSDictionary<String, Object>( NSArray<Object>, NSArray<Object> ) is
> undefined."
>
> NSDictionary<String, ? extends Object> tmpDict = new NSDictionary<String,
> Object>(
> new NSArray<Object>( new Object[] { location, schedType,
> Integer.valueOf(nWeekday) } ),
> new NSArray<Object>( new Object[] { "toLocation", "toScheduleType",
> "toDay.displayOrder" } ) );
>
>
>
> Roger
>
>
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