Re: [boost] Reflection library ?

From: remi.chateauneu_at_[hidden]
Date: 2007-05-13 17:06:26

Larry Evans a écrit :
> On 05/12/2007 04:23 PM, remi.chateauneu_at_[hidden] wrote:
> [snip]
>   
>> I do not know enough of this great library 'Fusion' to make a serious 
>> analysis, and BOOST_FUSION_ADAPT_STRUCT seems very close to what I did, 
>>     
>
> FWIW, I found the following two links useful for comparison:
>
>    For crd, see lines 29-42 of:
>
> http://crd.cvs.sourceforge.net/crd/crd/README?revision=1.4&view=markup
>
>    For fusion, see lines 39-43 of:
>
> http://boost.cvs.sourceforge.net/boost/boost/libs/fusion/test/sequence/adapt_struct.cpp?revision=1.2&view=markup&pathrev=HEAD
>   
Yes, crd's representation is heavier, although preprocessor macros could 
easily lighten it (but this is not the point I guess). Crd is a very 
modest library compared to Fusion and simply tries to focus on the needs 
I presented. Although it is very probably possible to do that with 
Fusion, crd is modelled after the need of some business applications to 
have an all-purpose definition of classes on which many commonly used 
algorithms would be 'plugged' onto. For example, this motivated the 
choice to use std::type_info * as unique key for all manipulation of 
members lists. This defines, for example, the column names of a table, 
with a std::map< const std::type_info *, std::string >.

There are, as well, two specific features I wish to implement:
- Loading classes definition from a compiled object files with debug 
information ( Please see this: 
http://www.garret.ru/~knizhnik/cppreflection/docs/reflect.html or what 
is returned by readelf), or from shareable libraries. This would target 
existing applications which cannot be modified for organisational or 
budget reasons.
- Given a dynamic class definition (list of members), creating an object 
with these members, but with a blob as underlying storage. The goal is 
to be able to manipulate class-like objets, with the same interface as a 
real class. ( ... maybe std::map< const std::type_info *, boost::any > , 
with type_info referring a class'member ? )  I agree that the concept is 
not quite clear at the moment, but again this is related to 
communicating data with software components which cannot be re-compiled 
at each modification of a user's class.

Thanks for your attention.

>> although the whole library seems more oriented towards compile-time 
>> operations ? 
>>     
>
> Well, according to:
>
>    the library is a "fusion" of compile time metaprogramming with runtime
>    programming.
>
> >from the page:
>
>    libs/fusion/doc/html/fusion/preface.html
>
> it should do both.  Of course I realize "seems more oriented towards
> compile-time  operations" is a "judgment call".  However,  it seems
> that the "basic operations" in both crd and fusion is accessing
> the I-th member in a tuple (or struct) and that the specific needs
> you mention below can be implemented using either the fusion
> "basic operations" or the crd "basic operations".  If that's true
> (i.e. the "basic operations" are the "basis of comparison") then
> fusion is just as runtime oriented as crd.
>
>   
>> My specific needs are:
>> - Iterations at run-time on class members, not only at compile-time, 
>> because some operations might be difficult to code (Trivial example: Add 
>> the latest ')' in a SQL query string). This implies, for example, that 
>> manipulation on a list of class members are done with plain STL algorithms.
>> - The possibility to add dynamic attributes for class members, indexed 
>> for example by typeid (Column names in a SQL table, or specific format 
>> for displaying a given class member), which may change from one object 
>> to another of the same class.
>> - The possibility to consider as a plain data member, any method 
>> (getter/setter ...) of a class, even if there is no underlying member, 
>> or if they are private, and also base classes.
>>  
>>     
> [snip]
>
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