Martin Wille wrote:
> Aleksey Gurtovoy wrote:
> ...
> > widget w2;
> > w.enable(boost::bind(&widget::is_enabled, &w2)); // here!
> > w2.enable(false);
> > assert(!w.is_enabled()) // !
> > }
> >
> > Pure & beautiful, IMO.
>
> Consider a widget class that performs some action on
> enabling/disabling (like dimming a button). In that case the
> action would be performed for w2 but not for w.
Oh, sorry for a confusion, 'enable' was a bad name for the method because I
didn't mean that semantics (and the whole example just wouldn't make much
sense).
It should have been 'is_enabled(bool_arg_t)' instead, because I was thinking
in terms of the model where the widget implementation itself _queries_ the
'widget' object's properties to perform the appropriate system actions, like
dimming a button.
So, the corrected example would be:
class widget
{
public:
// ...
typedef boost::function<bool ()> bool_arg_t;
self_t& is_enabled(bool_arg_t a_enabled); // note the signature!
bool is_enabled() const;
};
int main()
{
widget w;
w.is_enabled(true); // ordinary syntax/semantics
assert(w.is_enabled())
widget w2;
w.is_enabled(boost::bind(&widget::is_enabled, &w2)); // here!
w2.is_enabled(false);
assert(!w.is_enabled()) // !
}
I hope the name change makes the semantics of the above clearer.
Aleksey
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