Re: Registries [2]

Daniel Wallin <[email protected]> writes:

>> > Also, at least in lua. Modules could be loaded at any time, so there isn't
>> > really a point where we can assume everything is loaded and import
>> > converters.
>>
>>Can't you do something similar to the above?
>
> I don't think so. When I said "at any time" I didn't mean concurrently.
> Consider (lua code):
>
> loadmodule "X" -- exposes f(std::vector<double>)
> loadmodule "Y" -- exposes some convenience converters
>                 -- lua -> C++ std::vector<double>
>
> We would really like for module X to be able to use the converters
> introduced by module Y here, but module X is already initialized
> when module Y's converters are created.

The way I envisioned it:

    module X is loaded; loading_count = 1

    module X's initialization function imports converters from module
    Y, which causes Y to be loaded and initialized

    loading_count = 2

    Y registers its converters

    if Y imports converters from X, we notice that X is currently
    being initialized, and we push the request on a queue
    
    Y's initialization completes; loading_count = 1

    X registers its converters

    X's initialization completes; loading_count = 0

    Because loading_count = 0, we look at the import request queue
    and find the X->Y request.  We satisfy that.


>> >> >> > How are extensions to be registered in this central registry? In my
>> >> >> > previous post I proposed that they should be registered with a
>> >> >> > string literal identifier.
>> >> >> >
>> >> >> >    register_extension("my_extension");
>> >> >> >
>> >> >> > How does this fit in with pythons module system? (Note that we are
>> >> >> > really registering the extension, and not modules).
>> >> >>
>> >> >>Every extension is a module (not nececssarily the other way around),
>> >> >>so I see no reason not to register the extension by its module name
>> >> >
>> >> > I guess in python you can ask the interpreter state for the current
>> >> > module name?
>> >>
>> >>Erm, I'm not sure you can.  It is supplied as part of the module
>> >>initialization function; in fact, it is stored in the module object as
>> >>its __name__ attribute, so we can get it thence, assuming we can get
>> >>to the module.
>> >
>> > Ok.
>> >
>> >> > In lua this isn't possible though, so we would need some user defined
>> >> > identifier instead.
>> >>
>> >>You've gotta have the module or its name stored somewhere, dontcha?
>> >
>> > Other than in the .so filename? No.
>>
>>Why not just store it then?  When you create it, stick a string in its
>>__name__ attribute.
>
> I don't know what this means, create what? And what string? And how?
> :)

When you create the module, stick the name of the module in its name
attribute, e.g.

struct lua_module : lua_object
{
   lua_module(char const* name)
   {
        ...
        this->attr("__name__") = name;
        ...
   }
};

Also, take a look at the BOOST_PYTHON_MODULE macro.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com



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