Re: [boost] Any interest in static plugins?

Subject: Re: [boost] Any interest in static plugins?
From: Christian Schladetsch (christian.schladetsch_at_[hidden])
Date: 2009-11-30 07:17:45

Hi Dave,

I appreciate your effort with this.

However, it is uninteresting to me. Relying on static initialiser ordering
is a huge mistake which IMO cannot be fixed.

Factory models based on such approaches are doomed to failure. It is best to
explicitly make a factory and then explicitly add runtime types dynamically
(perhaps via a configuration file).

This is not only more correct (the order or registration is repeatable), it
preserves ideas of scope and removes requirements for globals.

Best,
Christian.

On Mon, Nov 30, 2009 at 3:34 AM, Dave van Soest <dsoest_at_[hidden]> wrote:

> Hi Christian, Darryl, and anyone else interested,
>
>  You may get more response if you posted or linked to some motivational
>>> examples.
>>>
>>
>> +1 on the examples. So far I'm merely intrigued to understand what the
>> library is/does.
>>
>
> Suppose that your program provides this simplified plugin interface class
> 'ObjectBase' in the header 'ObjectBase.hpp':
>
> ---- Start of code sample 1 ----
> class ObjectBase
> {
> public:
>    typedef std::string IdType;
>    ObjectBase() {}
>    virtual ~ObjectBase() {}
>    virtual void doSomething() = 0;
> };
> ---- End of code sample 1 ----
>
> Then the static plugin library will allow you to extend the functionality
> of this program merely by adding a separate source file containing the
> following code:
>
> ---- Start of code sample 2 ----
> #include <static_plugin.hpp>
> #include "ObjectBase.hpp"
>
> class SomeObject : ObjectBase
> {
>    void doSomething() { std::cout << "Doing something" << std::endl; }
>    static const IdType id;
> };
>
> const SomeObject::IdType SomeObject::id = "SomeObject_ID";
> static const static_plugin::Creator<SomeObject, ObjectBase> myPlugin;
> ---- End of code sample 2 ----
>
> The above code causes a factory for the 'SomeObject' class to be created
> automatically and registered with the factory manager for classes
> implementing the 'ObjectBase' interface. This all happens when the program
> is just started (before it enters 'main').
>
> The factory manager for 'ObjectBase' derivatives, which follows the
> singleton pattern, can be used from your program as follows (note: again
> this code is simplified):
>
> ---- Start of code sample 3 ----
> #include <static_plugin.hpp>
> #include "ObjectBase.hpp"
>
> typedef FactoryManager<ObjectBase> ObjectBaseFM;
>
> int main(void) {
>    const ObjectBaseFM& fm(getFactoryManager<ObjectBase>());
>    assert(fm.factoryCount() > 0);
>    ObjectBase::IdType id(fm.factoryIdList().at(0));
>    std::auto_ptr<ObjectBase> object(fm.create(id));
>    object->doSomething();
>    return 0;
> }
> ---- End of code sample 3 ----
>
> The only requirements are that ObjectBase defines the IdType type and
> SomeObject contains a static member of type IdType called 'id'. The
> declaration of the static_plugin::Creator<...> causes the SomeObject plugin
> to be registered.
>
> Sidenote: I just tested this functionality in a dynamically loaded library
> and that works now too. This means that any plugin in your dynamic library
> is automatically registered without the need to call some 'initLibrary'
> function in the library.
>
> _______________________________________________
> Unsubscribe & other changes:
> http://lists.boost.org/mailman/listinfo.cgi/boost
>