Boost C++ Libraries: Ticket #10443: [fusion] Compile errors with boost::fusion::invoke and boost::result_of using decltype

Tue, 02 Sep 2014 14:26:18 GMT

This was my original stackoverflow question about this problem: http://stackoverflow.com/questions/25621676/boostfusioninvoke-compiler-error-with-visual-studio-2013

summary changed

Tue, 02 Sep 2014 14:37:14 GMT

summary Compile errors with boost::fusion::invoke and boost::result_of using decltype → [fusion] Compile errors with boost::fusion::invoke and boost::result_of using decltype

Fri, 05 Sep 2014 17:53:03 GMT

We have discussed this on IRC with alfC, and come to the conclusion that the underlying issue is that result_of::invoke is not SFINAE-friendly (as defined by C++11). The proper fix for this issue is then to make it SFINAE-friendly for all C++ versions.

Additionally, there are two invoke definitions: one for Sequence& and another one for Sequence const&. This is redundant at best, and should be simplified.

Michel Morin — Sat, 06 Sep 2014 03:14:35 GMT

I've not followed recent updates in Boost.Fusion, so I might be wrong, but...

Both C++03 and C++11 versions of fusion::invoke are not SFINAE-friendly, as demonstrated in this post ( Re: [result_of] now uses decltype on release branch ):

#include <boost/fusion/include/invoke.hpp>
#include <boost/fusion/include/vector.hpp>
struct F {
    template <typename Sig>
    struct result;
    template <typename This>
    struct result<This(int&)>
    {
        typedef void type;
    };
    void operator()(int&) const {}
};
int main (int argc, char* argv[])
{
    boost::fusion::vector<int> v(1);
    // Error;
    // trying to instantiate result_of<F(const int&)>
    boost::fusion::invoke(F(), v);
    return 0;
}

Sun, 19 Oct 2014 17:50:51 GMT

Note I hit a very similar issue (#10676) with boost::fusion::fold. I think there's a general issue with fusion's "result_of" detail classes (boost::fusion::result_of::Stuff) not being SFINAE compatible.

cc set

Sun, 19 Oct 2014 17:52:28 GMT

cc jaredgrubb@… added

status changed; resolution set

Joel de Guzman — Sun, 19 Oct 2014 22:25:34 GMT

status new → closed
resolution → fixed

Fixed now in develop branch. invoke is now sfinae friendly. Please check to be sure.

cc, status changed; resolution deleted

Wed, 22 Oct 2014 11:05:27 GMT

cc flast@… added
status closed → reopened
resolution fixed

I think djowel's fix is incomplete. I open a pull-request to fix this issue completely.

Please check it. ttps://github.com/boostorg/fusion/pull/24

status changed; resolution set

Joel de Guzman — Fri, 12 Jun 2015 06:49:09 GMT

status reopened → closed
resolution → fixed