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From Simone Tripodi <simonetrip...@apache.org>
Subject Re: [chain][v2] clever context
Date Fri, 09 Sep 2011 21:14:38 GMT
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 <pbenedict@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 <simonetripodi@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 <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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>>>
>>
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>>
>
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