indeed, the retrieve method would allow users assigning retrieved object to all T that extend V, like the ClassToInstanceMap, take a look at the method signatures[1]
[1] http://s.apache.org/Mno http://people.apache.org/~simonetripodi/ http://www.99soft.org/ On Fri, Sep 9, 2011 at 11:02 PM, Paul Benedict <pbened...@apache.org> wrote: > The purpose of Generics is to provide type safety with the implicit > casts. Implicit casts because of typing shouldn't cause a > ClassCastException. That would break an important principle behind > using gnerics. Are you sure Guava is doing what you're proposing? > Typing should always be safe; I would be surprised if they would allow > unsafe implicit casts. > > On Fri, Sep 9, 2011 at 3:34 PM, Simone Tripodi <simonetrip...@apache.org> > wrote: >> Hi Paul, >> the type inference becomes more interesting and useful if you think to >> more complicated context instances, take as sample the Guava's >> ClassToInstanceMap[1] where values extend a specific base type. >> >> the <T extends V> in the `retrieve` method reduces anyway the number >> of errors, given an hypothetically Context<String, Number> users >> cannot cast to a different type: >> >> MyPojo myPojo = (MyPojo) context.get( "myKey" ); >> >> I think anyway putting types to Context would make Filter, Command, >> Chain, ... classes over engineered IMHO >> >> best, >> Simo >> >> [1] http://s.apache.org/xfj >> >> http://people.apache.org/~simonetripodi/ >> http://www.99soft.org/ >> >> >> >> On Fri, Sep 9, 2011 at 10:20 PM, Paul Benedict <pbened...@apache.org> wrote: >>> On Fri, Sep 9, 2011 at 3:15 PM, Elijah Zupancic <eli...@zupancic.name> >>> wrote: >>>> Specifying Object for V would be the most likely use case. >>>> >>>> On Fri, Sep 9, 2011 at 1:12 PM, Paul Benedict <pbened...@apache.org> wrote: >>>>> On Fri, Sep 9, 2011 at 3:06 PM, Simone Tripodi <simonetrip...@apache.org> >>>>> wrote: >>>>>> Hi Paul, >>>>>> the use of that method is to automatically infer the assigned type, >>>>>> instead of writing >>>>>> >>>>>> MyPojo myPojo = (MyPojo) context.get( "myKey" ); >>>>>> >>>>>> the retrieve method allows to >>>>>> >>>>>> MyPojo myPojo = context.retrieve( "myKey" ); >>>>>> >>>>> >>>>> Hmm... The inference should be automatic unless you specified Object for >>>>> type V: >>>>> Context<String, String> properties = new ContextBase<String, String>(); >>>>> String value = properties.retrieve("myKey"); >>>>> >>> >>> I don't have a good answer for the problem. I just think if you >>> declare types <K, V> at the class level, those should be the types >>> used on the methods too. The problem that I have with <T extends V> is >>> that it assumes a type-safe cast. You are right to say >>> ClassCastException was thrown for both of your examples but <T extends >>> V> breaks the "rule" that generics should be type-safe casts. It's >>> better to have the user create a bum cast and fail then the compiler >>> infer a bum cast and fail, imo. >>> >>> Paul >>> >>> --------------------------------------------------------------------- >>> To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org >>> For additional commands, e-mail: dev-h...@commons.apache.org >>> >>> >> >> --------------------------------------------------------------------- >> To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org >> For additional commands, e-mail: dev-h...@commons.apache.org >> >> > > --------------------------------------------------------------------- > To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org > For additional commands, e-mail: dev-h...@commons.apache.org > > --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@commons.apache.org For additional commands, e-mail: dev-h...@commons.apache.org
