Fwd: [Boost-users] Can you compare boost::function objects?

From: Stuart Dootson (stuart.dootson_at_[hidden])
Date: 2005-05-27 08:13:31

On 5/27/05, Douglas Gregor <doug.gregor_at_[hidden]> wrote:
> 
> On May 27, 2005, at 6:10 AM, Stuart Dootson wrote:
> 
> > I'm not certain (from the documentation) whether see if two
> > boost::function objects are equal (I tend to think not!).
> 
> Sounds like I need to fix the documentation.
> 
> > The code
> > below doesn't compile on VC7.1, raising an error about 4 ambiguous
> > overloads of operator==
> >
> > #include <boost/function.hpp>
> >
> > int Flip() { return 2; }
> >
> > int main(int,char**)
> > {
> >    boost::function<int()> f1 = &Flip;
> >    boost::function<int()> f2 = &Flip;
> >    bool const areTheyEqual = (f1 == f2);
> > }
> >
> > Can someone confirm if this should/should not compile, please?
> 
> It should not compile. Comparison of two function<> objects is not
> implementable in genera (without compiler extensions or significant
> user pain).
> 
>         Doug
> 

Thanks, Doug - that's pretty much what I thought (just wasn't 100%
sure). The tutorial sub-title 'Comparing Boost.Function function
objects' kind of implies that you can compare Boost.Function objects
with each other. The text under that sub-title does say that you can
compare a Boost.Function object with any function object that can be
contained in a Boost.Function object (but can a Boost.Function contain
a Boost.Function?). There's no explicit statement there, though, that
says you can't compare a Boost.Function object with another
Boost.Function object.

Heh - just looked at the reference - the operator== description does
say that functionN objects aren't EqualityComparable. Doh!

Stuart