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
