2011/6/27 Ben Robinson <icaretaker@gmail.com>:
The purpose of auto_ptr is to clean up the instance automatically. It was a design goal to make destruction of the Singularity explicit, especially in multi-threaded contexts. However, users can create custom ThreadingModel policies which use any kind of smart pointer they desires. I thought to provide the only a primitive pointer for the included policies.
It is a good thing, to have an explicit destructor, but we must call destructor in case, when user forgets to call destruction or when the program suddenly exits. Consider the following example: DescriptorThatMustBeClosed & horizon = DescriptorThatMustBeClosed::create(&event); ... function_that_calls_exit(); ... DescriptorThatMustBeClosed::destroy(); Moreover, auto_ptr is primitive enough and will not make the performance worse.
The recommended usage of Singularity is without a globally accessible get() function, so the performance of create() and destroy() should not be an issue. If global_access is enabled, it would be advisable to minimize calls to get(), such as calling get() once per thread, storing the result in thread-local storage.
Than it is OK. More remarks: 1) it is a common practice to put all the support structures and variables to namespace boost::detail 2) Overload the virtual const char* what() const throw(); function for all your exceptions (struct singularity_already_created, already_destroyed, singularity_not_created, singularity_destroy_on_incorrect_threading ) 3) Back to the question with auto_ptr. It looks like there is no need in specifying the ptr_type. You always return references, user can't get access to the pointer directly. So, all you need is to hold the pointer and take care of freeing resources, if user forget to do it. And std::auto_ptr looks like a great thing for such cases Best regards, Antony Polukhin