Re: Is it necessary to use singleton pattern?

From:

Thiago Adams <thiago.adams@gmail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Thu, 3 Feb 2011 09:14:39 CST

Message-ID:

<81c71553-c66d-4b00-b013-4a0991291307@y12g2000prf.googlegroups.com>

i am currently developing a wrapper library, which is suppose to
provide call backs to
application developers with events of different category.

my thought is.. use a singleton class and hold user registered
call-back derived class object
and call the object when-ever i get events.

Now to just hold a call-back object pointer do i need a singleton
class instance?.

Is there better approach?.

my thoughts look something like:

class baseCB
{
public:
virtual event1(const msg1 &msg);
virtual event2(const msg2 &msg);

};

class wrapper
{
static wrapperInstance() { return s_wrapperInstance; }
static initialize(baseCB *pCB) { s_wrapperInstance = new wrapper(pCB);
baseCB *callback() { return m_cb; }
private:
explit wrapper(baseCB *pCB):m_cb(pCB){}
baseCB *m_cb;

};

in the place where i get events i want to do something like:

wrapperInstance()->callback()->event1(&msg);

My suggestion is to call the event interface directly in the place you
receive the events.

void CallEventReceiver( event_arguments , baseCB* pEventReceiver)
{
   pEventReceiver->Call1(?);
   pEventReceiver->Call2(?);
}

Here pEventReceiver is your baseCB. (I would suggest changing this
name as well; "base" is too generic)

Then you can implement an especial pEventReceiver class to be your
router (new class derived from baseCB) and dispatch messages for the
registered pEventReceivers.

Doing like this, everything is an implementation detail around the
interface.

You can choose what is better for you depending of the data structures
you already have.
Maybe is a good idea to make the "pEventReceiver router" a singleton.

I personally don?t like to make classes aware if they singletons or
not.
I prefer to leave this decision to the instantiation.

----
http://www.thradams.com/

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