Re: [boost] [any] boost::get style accessors

Subject: Re: [boost] [any] boost::get style accessors
From: vicente.botet (vicente.botet_at_[hidden])
Date: 2010-04-29 13:26:50

----- Original Message ----- 
From: "Stefan" <mstefanro_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Thursday, April 29, 2010 6:50 PM
Subject: Re: [boost] [any] boost::get style accessors

> 
> vicente.botet wrote:
>> ----- Original Message ----- 
>> From: "Christoph Heindl" <christoph.heindl_at_[hidden]>
>> To: <boost_at_[hidden]>
>> Sent: Thursday, April 29, 2010 5:50 PM
>> Subject: Re: [boost] [any] boost::get style accessors
>> 
>> 
>> 
>> On Thu, Apr 29, 2010 at 1:10 PM, Stewart, Robert <Robert.Stewart_at_[hidden]> wrote:
>>> Christoph Heindl wrote:
>>>> On Wed, Apr 28, 2010 at 8:00 PM, Stewart, Robert
>>>> <Robert.Stewart_at_[hidden]> wrote:
>>>>
>>>>> At that point, I think they should be on par with any_cast
>>>>> rather than built on any_cast so that exceptions needn't be
>>>>> translated. Exception handling overhead is too costly to do
>>>>> it twice when it isn't necessary.
>>>> I agree. I don't see any added value by using bad_get, except all
>>>> boost:get accessors would throw bad_get exceptions.
>>> Perhaps you missed my point. I was suggesting that your gets be implemented at the same level of access as any_cast so no exception translation were needed. In other words, take code straight from any_cast and use it to implement get, provided bad_cast is deemed useful.
>> 
>> Indeed I did. In boost 1.42 this corresponds to duplicating ~40 lines
>> of code to exchange the type of exception thrown. I'm not too keen of
>> doing this (not talking about the tests I would have to duplicate too)
>> :) Of course, code could be refactored to refer to a common set of
>> methods that take the exception to throw as templated argument, if
>> desired.
>> 
>> _______________________________________________
>> +1 for refactoring.
>> 
> It would make little sense to have a boost::get working with both 
> Boost.Variant and Boost.Any transparently if it does not have a 
> consistent behavior (i.e. the same way of signaling a problem). I don't 
> think refactoring some code to make the behavior consistent will be 
> problematic.
> Currently, boost::bad_get is deriving directly from std::exception 
> whereas boost::bad_any_cast is deriving from std::bad_cast. It might 
> make more sense to have both boost::bad_get and boost::bad_any_cast 
> derive from a common exception class type, such as boost::bad_cast (or 
> maybe have boost::bad_get derive from std::bad_cast)

I was talking only on refactoring the code on Boost.Any for the functions get and any_cast ;-)

Thinking a little bit more the introduction of boost::get<> in Boost.Any would  result at the end on the deprecation of any_cast, isn't it? So the refactoring at the interface level will introduce constraints that sould be avoided.

Best,
Vicente

Vicente