Subject: Re: [boost] [Boost.utility]
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2010-01-26 10:57:05
Andrew Chinkoff wrote:
> > However, I've always thought the better interface was via a
> > smart pointer. Upon construction, the smart
> > pointer would access the Singleton instance and cache it in
> > a data member. Subsequent access via
> > operator ->() or operator *() would use the data member,
> > thus avoiding the overhead of the instance accessor.
> I think this is unnecessary. The very simple and obvious way
> is access via reference, don't it?
I think you missed the point. A typical spelling is some_singleton_class::instance(). That member function must determine whether the Singleton has been instantiated and that, often in a thread safe way. Thus, there's a function call and some sort of synchronized access/manipulation of state. That's costly.
In my version, that cost is paid once per context by the smart pointer constructor. All accesses via that smart pointer *do not* incur the instance() overhead.
> > They do access global state, but there often is global state in an
> > application. If Singletons provide the only > means to
> > access state, they
> > formalize that access. Singletons can also, using policies, control
> > lifetime, post-destruction behavior, etc.
> It it really true.
> > Consequently, Singletons are more than a crutch, though
> > often overused, abused, or misused.
> I disagree.
Given your agreement with the foregoing, can I assume your disagreement is with the "often overused, abused, or misused" statement? If so, we're at an impasse. My experience has shown that Singletons are often overused, abused, or misused. Please note that I did not write that they are always so treated.
Rob Stewart robert.stewart_at_[hidden]
Software Engineer, Core Software using std::disclaimer;
Susquehanna International Group, LLP http://www.sig.com
IMPORTANT: The information contained in this email and/or its attachments is confidential. If you are not the intended recipient, please notify the sender immediately by reply and immediately delete this message and all its attachments. Any review, use, reproduction, disclosure or dissemination of this message or any attachment by an unintended recipient is strictly prohibited. Neither this message nor any attachment is intended as or should be construed as an offer, solicitation or recommendation to buy or sell any security or other financial instrument. Neither the sender, his or her employer nor any of their respective affiliates makes any warranties as to the completeness or accuracy of any of the information contained herein or that this message or any of its attachments is free of viruses.
Boost list run by bdawes at acm.org, gregod at cs.rpi.edu, cpdaniel at pacbell.net, john at johnmaddock.co.uk