Re: [Boost-users] [fusion]Is it possible to wrap a function template into a function object?

Subject: Re: [Boost-users] [fusion]Is it possible to wrap a function template into a function object?
From: Nathan Ridge (zeratul976_at_[hidden])
Date: 2011-08-11 21:43:56

> > If there is a function template:
> > template<typename T> T f(T t);
> > then f is not a type and cannot be passed to fusion::for_each() as the
> > second argument.
> > But I can't write fusion::for_each(someSequence,&f<SomeType>) either since
> > elements of someSequence has different types.
> > While I can write f as a functor fo
> > struct fo{ template<typename T> T operator()(T t); };
> > and call fusion::for_each(someSequence,fo()), sometimes I need to use
> > function templates in libraries ( say, I have a fusion::vector whose
> > elements are ranges ) and the only solution seems to be writing a lot of
> > functors to wrap the function templates. I tried to find a wrapper class
> > template that can wrap arbitary function templates to functors in boost but
> > I didn't find any. Then I tried to write such a wrapper using constructs
> > like
> > template&lt;template&lt;typename T0&gt; class F>struct temp_fun_1;
> > but the code made my MSVC2008 compiler crash(really!). Is there such a
> > wrapper in boost or any other library, or is it even possible?
>
> fusion::for_each is easy because the expected function only needs to
> return void. It gets more complex if you have to return something,
> e.g. fusion::fold. You really need a Polymorphic Function Object
> (http://tinyurl.com/3qpsrkc) with proper result_of facilities.
> Anything less won't cut it.
>
> Wrapper? There's nothing close to what you want primarily due to
> the complexities of the return type deduction. It won't make sense
> to provide an easy wrapper for monomorphic return types which is
> only useful for for_each.

What if we use C++0x decltype for return type deduction?

Is it possible then?

Thanks,
Nate