Boost logo

Boost :

Subject: Re: [boost] [Boost.utility]
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2010-01-26 09:40:15


Jeff Flinn wrote:
>
> I've always been mystified as to why a singleton instance is accessed
> via pointer rather than by reference. Singleton models a
> one-and-only-one relationship a pointer models a zero-or-one
> relationship.

I've often thought the same. 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.

> That said, in my experience singletons are
> generally used as a crutch to access global state.

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. Consequently, Singletons are more than a crutch, though often overused, abused, or misused.

_____
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