Re: [boost] [Boost.utility]

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

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