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From Simone Tripodi <simonetrip...@apache.org>
Subject Re: [chain][v2] clever context
Date Fri, 09 Sep 2011 20:34:33 GMT
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 <pbenedict@apache.org> wrote:
> On Fri, Sep 9, 2011 at 3:15 PM, Elijah Zupancic <elijah@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 <pbenedict@apache.org> wrote:
>>> On Fri, Sep 9, 2011 at 3:06 PM, Simone Tripodi <simonetripodi@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
>
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