🚀 go-pugleaf

In article <009A0041E919D6E0.3D60EEDA@ittpub.nl> "Wil Evers"
<wil@ittpub.nl> writes:

|> In article <KANZE.96Mar27134634@gabi.gabi-soft.fr> kanze@gabi-soft.fr (J.
|> Kanze) writes:

|> >     class X
|> >     {
|> >     public :
|> >         enum DontInit { dontInit } ;
|> >                         X( DontInit )   {}
|> >                         X() : i( 5 )    {}
|> >     private :
|> >         int             i ;
|> >     } ;
|> > 
|> > Objects to be initialized by the nifty_counter would be defined thus:
|> > 
|> >     X               obj( X::dontInit ) ;
|> > 
|> > Nifty counter then becomes:
|> > 
|> >     class NiftyCounter
|> >     {
|> >         static int          cnt ;
|> >     public :
|> >                             NiftyCounter()
|> >         {
|> >             if ( cnt == 0 )
|> >                 new( &obj ) X ;
|> >             cnt ++ ;
|> >         }
|> >     } ;
|> > 
|> > (Note that for NiftyCounter to work, it is absolutely essential that the
|> > definition of the object invoke a no-op constructor, since the object
|> > may in fact already be constructed.)
|> > 
|> > As you can see, this works equally well for const objects.

|> I don't think so. For this to work on a const object, you would at least have
|> to cast away its constness - after all, the standard placement new operator
|> takes a void * as its second argument, not a const void *.

You're right.  I'm getting careless.  (And the last time I did this, my
compiler still didn't enforce const-ness in this case.)

|> In my opinion, the `dummy constructor' technique is fundamentally bad. It
|> requires that all base classes and member variables have dummy constructors
|> too, so it is not always applicable.

|> When I use the nifty counter idiom, I normally construct the global
|> object in a suitably aligned raw memory buffer (a character array).
|> Users access the constructed object through a properly typed global
|> reference pointing to the raw memory buffer.

IMHO, the nifty counter idiom is in general not very good.  I much
prefer to avoid the global or class static, and require the user to call
a function which returns a reference to a local static.
-- 
James Kanze           (+33) 88 14 49 00          email: kanze@gabi-soft.fr
GABI Software, Sarl., 8 rue des Francs Bourgeois, 67000 Strasbourg, France
Conseils en informatique industrielle --
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