Re: [boost] [Boost.utility]

Subject: Re: [boost] [Boost.utility]
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2010-01-26 14:41:48

vicente.botet wrote:
>
> What about defining all the functions of the singleton at a
> namespace level. So rather than doing
>
> struct S : singleton<S> {
>     void f1();
>     int f2(char);
> };
>
> and use it as
>
> S::instance().f1();
>
> doing in this way
>
> namespace S {
>     void f1();
>     int f2(char);
> };
>
> and use it as
>
> S::f1();
>
> Of course, nothing forbids the implementation of the
> functions at the namespace level to use a singleton, but this
> is an internal detail, not shown at the user level.
>
> What use cases do you see where the class interface is more
> convenient than the namespace interface?

What you've shown is simply a variation of Monostate.  What's missing is any opportunity to inline functions because the state must be in the implementation file.  (The state could be put in an "off limits" nested namespace, but that's easy to violate, so a poor design.)

Aside from the possible loss of efficiency, there's no great disadvantage, though some Singleton designs allow for objects that are destroyed by atexit(), that can be resurrected if needed after being destroyed (due to another static scope object outliving the first instance), etc.  Most of those things are overly complicated, however.

_____
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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