Re: [boost] [review] Fast track review of Boost.Utility/Singleton begins today

From: Giovanni Piero Deretta (gpderetta_at_[hidden])
Date: 2008-01-17 12:27:14

On Jan 17, 2008 6:06 PM, Gennadiy Rozental <rogeeff_at_[hidden]> wrote:
> Anthony Williams <anthony_w.geo <at> yahoo.com> writes:
> >
> > A singleton enforces that there is only one global instance with global
> > accessibility. If you just create one (and pass it down by dependency
> > injection)
> > then the decision to just create one is made at the top level (where it
> > belongs), and the client code doesn't have to be fussed with how many
> > instances
> > there are --- just that it can use the one provided.
> >
> > void some_function(Logger& logger)
> > {
> >    logger.log("something");
> > }
> >
> > int main()
> > {
> >   Logger myLogger; // ooh look, just one
> >   some_function(myLogger);
> > }
>
> This design has obvios drawback, right: you need to pass the instance around.

Some consider this a feature.

> Global free function is as bad as global variables IMO and as bad as singlton
> for what it worth.

How is a global free function is as bad as a global variable? You
cannot mutate a function,
while you can certainly mutate a variable. What is bad is not the
visibility, but the mutability.
(I do not think anybody has problems with global constants).
I agree that a global variable is as bad as a singleton, though.

--
gpd