Re: [Boost-users] more lambda issues

From: Joaquín Mª López Muñoz (joaquin_at_[hidden])
Date: 2006-11-30 11:39:05

Peter Dimov ha escrito:

> Joaquín Mª López Muñoz wrote:
> > Noah Roberts ha escrito:
> >
> > [...]
> >
> >> So in the end, my problem is thus:
> >>
> >> std::find_if(cont.begin(), cont.end(), bind(&deref_val_type::f, _1)
> >> == 5);
> >>
> >> How is that accomplished with lambda if cont holds smart pointers?
> >> So far I haven't found any way...
> >
> > OK, you can write it with Boost Lambda as follows:
> >
> > namespace l = boost::lambda;
> >
> > std::find_if(
> >   cont.begin(), cont.end(),
> >   l::bind<int>(&*l::_1->*&deref_val_type::f)==5);
>
> bind( &deref_val_type::f, *_1 ) == 5 may work with Lambda.

Almost: the translation of the expression to the lambda world, i.e.

  l::bind( &deref_val_type::f, *l::_1 ) == 5

(assuming namespace l = boost::lambda) fails to compile because
it indices the declaration of

  boost::tuples::cons<deref_val_type, boost::tuples::null_type>::head

which is not instantiable deref_val_type is abstract. The closest I
can get in BLL to your formulation is:

  l::bind( &deref_val_type::f, &*l::_1 ) == 5

which works as expected.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo