Re: [boost] Re: Multiton

From: Jason Hise (chaos_at_[hidden])
Date: 2005-01-26 11:13:25

Jason Hise wrote:

> Alright... I believe that my multiton dependency lifetime is 
> functional based on a few simple tests.  However, I could easily be 
> wrong, so I would appreciate the efforts of everyone who tries to 
> break my code.  My next task will be to try a multiton longevity 
> lifetime policy, and then perhaps I'll try to find a way to make 
> GetInst accept multiple keys.  The code at 
> http://boost-sandbox.sourceforge.net/vault/ under Singleton is up to date.

I just realized that I should probably at least provide a small sample 
program so that people can see how the multiton is intended to be used.  
In the following example, a unique country can exist for each unique 
name, a unique state can exist for each unique name, and states depend 
upon the country "USA".

#include <string>
#include <Multiton.h>
using namespace boost::singleton;

class Country : public Multiton < std::string, Country >
{
protected:
    Country (  )
    {
    }

    ~ Country (  )
    {
    }
};

// uncomment to enable lazy creation
class State : public Multiton < std::string, State/*, 
MultitonDependencyLifetime < std::string, State, true >*/ >
{
private:
    // guarantee that the USA is created immediately
    // before the creation of the first state
    Country::LifetimePolicy::Dependency require_usa;

protected:
    State (  ) : require_usa ( "USA" )
    {
    }

    ~ State (  )
    {
    }
};

void f (  )
{
    // this creates the ohio instance only if lazy creation is false
    State::LifetimePolicy::Dependency require_oh ( "Ohio" );

    {
        // this creates the ohio instance if it has not been created yet
        State::Pointer ohio = State::GetInst ( "Ohio" );
        // this creates the florida instance
        State::Pointer florida = State::GetInst ( "Florida" );
    }
    int i = 5;
    // florida has been destroyed
    // but dependency on ohio is still in scope, so ohio lives on
}
// ohio is destroyed, after which point the USA is destroyed
// if it is desired for these things to live to the end of the program,
// just add static dependencies, ex:
// Country::LifetimePolicy::Dependency require_usa ( "USA" );

int main (  )
{
    f (  );
    return 0;
}