Re: [boost] Re: Re: bald singleton pointers

From: Jason Hise (chaos_at_[hidden])
Date: 2005-02-14 23:54:11

Pavel Vozenilek wrote:

>Maybe function
>
>template<.....>
>T* unsafe_get_pointer(singleton<T>::pointer&) { ... }
>
>would be enough. Having one more class
>for just one function feels as overkill.
>
>Local need for raw pointer should not mean
>possibly global change in design.
>
>/Pavel
>
I'm terribly torn on this issue.

Use of a raw singleton pointer is dangerous if it remains in use for a 
long period of time, specifically long enough for the instance to have a 
possibility of being destroyed.  If the singleton uses a real locking 
policy the code using the raw pointer would have to lock the operations 
manually.

On the other hand, a raw pointer is the only really feasible way to pass 
a singleton pointer as a pointer to a non singleton base class.  Example:

class LoggerBase
{
public:
    virtual void Log ( const char * msg ) = 0;
};

class GlobalLog : public singleton < GlobalLog >, public LoggerBase
{
public:
    virtual void Log ( const char * msg )
    {
        // write to file or something
    }
};

void PerformOperation ( vector < LoggerBase * > listeners, /*other 
operands*/ )
{
    if ( shit_happens )
    {
        // use lambda and for_each to write a message to each log in 
listeners
        // (I don't know the lambda library so I can't write this code 
myself.  I should take next weekend to learn it, it looks really handy)
    }
}

Thus, at this point my thought is that the C++ motto is 'trust the 
programmer', so I'm thinking I should just provide the unsafe_raw_ptr (  
) member in the singleton, surround it with comments in all caps, and 
document the heck out of it.

-Jason