Re: [Boost-users] more lambda issues

From: Joaquín Mª López Muñoz (joaquin_at_[hidden])
Date: 2006-11-30 04:29:25

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);

Boost.Bind is smarter here, since Boost Lambda needs assistance in:

1. Determining the return type of deref_val_type::f (hence the <int> in
l::bind<int>.)
2. Dereferencing the shared_ptr, hence the use of &*l::_1 to get a plain
pointer
from the shared_ptr, combined with ->* to call deref_val_type::f

Others might find terser ways to express this with Boost Lambda, but
looks like Boost.Bind is a clear winner here.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo