Re: [boost] MPL's "round" lambda

From: Terje Slettebø (tslettebo_at_[hidden])
Date: 2003-03-11 02:28:49

A few months ago, Aleksey posted a cool way of doing lambda using function
notation. I hadn't followed the thread at the time, but I read up on it
recently. Like many others, I found it hard to understand how it worked, so
I asked Aleksey if he could make a minimal example of it, which he did.

For the benefit of anybody else interested in knowing how it works, I post
the example here. I found it much easier to understand how it works, with
such a minimal example.

--- Start ---

#include <boost/mpl/quote.hpp>
#include <boost/mpl/apply.hpp>
#include "boost/mpl/bind.hpp"
#include "boost/type_traits/is_same.hpp"
#include "boost/static_assert.hpp"

using namespace boost::mpl;

template<typename T>
struct expr
{
  typedef T type;
};

template<typename F, typename T1, typename T2>
struct expr<F (T1, T2)> : bind2<F, typename expr<T1>::type, typename
expr<T2>::type> {};

struct is_same : quote2<boost::is_same> {};

// Here:

typedef apply<expr<is_same(_, int)>, int>::type type;

BOOST_STATIC_ASSERT(type::value);

--- End ---

Regards,

Terje