Thanks for the reply, Steven. You were able to give me enough direction to solve the problem. I simply had to write a wrapper class around apply that had the correct template signature. template <typename MetaFunc> struct apply1 { template <typename T> struct apply : MetaFunc::apply<T> {}; }; int main(void) { test< apply1< boost::mpl::lambda< boost::is_same<boost::mpl::_1, int> >::type >::apply >::print(); }; I've gotta say, though, that this behavior of MPL's lambda, bind, quoten, etc Meftafunctions is counter intuitive (to put it nicely). The runtime bind library, as a counter example, is intuitive. When you bind one argument to a second order function, you get a first order function. If the runtime bind library was designed similar to the bind facility in MPL, it would give you a function with a variable argument list, which I believe anyone would agree is counter intuitive. I'm sure there is a good reason MPL was designed this way, though I doubt its a better reason than the reason it should have been designed intuitively. -Matt On Thu, Mar 13, 2008 at 9:31 AM, Steven Watanabe <watanabesj@gmail.com> wrote:
AMDG
Matt Brown wrote:
I just tried to build this code in visual studio 2005, and got error:
error C3201: the template parameter list for class template 'boost::mpl::bind2<F,T1,T2>::apply' does not match the template parameter list for template parameter 'boolfunc'
This code works fine with gcc, and boost mpl portability page (http://www.boost.org/libs/mpl/doc/tutorial/portability.html) says my version of visual studio should be able to compile this. However, it appears to think the lambda< ... >::type::apply is not a metafunction. Any help will be greatly appreciated.
-Matt Brown
#include <iostream> #include <boost/mpl/lambda.hpp> #include <boost/type_traits/is_same.hpp> #include <boost/mpl/placeholders.hpp>
template <template <typename> class boolfunc> class test { public: static void print() { if(boolfunc<int>::type::value) { std::cout << "int: true\n"; } } };
int main(void) { test< boost::mpl::lambda< boost::is_same<boost::mpl::_1, int> >::type::apply >::print(); };
Don't do that.
boost::mpl::lambda< boost::is_same<boost::mpl::_1, int> >::type::apply<int>::type
will work, but apply actually takes extra default arguments and thus cannot be bound to a template template argument.
i.e. (For exposition only)
template<class T> struct lambda { struct type { template<class T0 = na, class T1 = na, ...> struct apply { typedef /unspecified/ type; }; }; };
In Christ, Steven Watanabe
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