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From Simone Tripodi <simonetrip...@apache.org>
Subject Re: [chain][v2] clever context
Date Fri, 09 Sep 2011 21:52:07 GMT
I honestly still haven't figured out how our Context should look
alike, better if I go sleep (it's almost midnight here in Italy :P)
and thinking about it :)
Good night, I'll come back writing tomorrow!
Simo

http://people.apache.org/~simonetripodi/
http://www.99soft.org/



On Fri, Sep 9, 2011 at 11:32 PM, Paul Benedict <pbenedict@apache.org> wrote:
> Definitely interesting. I think this might be a special case though;
> ClassToInstanceMap is dedicated to class instances which is probably
> why they extended Map so that it has extra guarantees. I don't know if
> such a pattern is advisable for a regular key/value pair. What are
> your thoughts?
>
> On Fri, Sep 9, 2011 at 4:14 PM, Simone Tripodi <simonetripodi@apache.org> wrote:
>> 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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>>
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>>
>
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