[boost] [type_erasure] call with multiple placeholders

Subject: [boost] [type_erasure] call with multiple placeholders
From: Benedek Thaler (thalerbenedek_at_[hidden])
Date: 2014-07-24 18:12:12

Hi,

I have the following type erasure setup:
https://github.com/erenon/pipeline/blob/type_erasure/include/boost/pipeline/type_erasure.hpp

I'd like to make `any` have a method template, `connect_to`, i.e:

class any {
  template <typename T> auto connect_to(const T&) {}
}

I have a concept, added to the main concept like this:

detail::has_connect_to<type_erasure::_self, type_erasure::_a>

And also a concept_interface specialization. (Bottom of the file in the
link above)

The doc says:
"When there are multiple placeholders involved, you will have to use tuple,
or pass the bindings explicitly, but the substitution still works the same
way. "

I'm trying to do just like this, but without success. Errors include:

error: ‘const struct boost::type_erasure::_self’ has no member named
‘connect_to’

error: ‘apply’ is not a member of
‘boost::pipeline::detail::has_connect_to<boost::type_erasure::_self,
boost::type_erasure::_a>’

*error: no matching function for call to
‘call(boost::type_erasure::concept_interface<...[snip]...>`*

I think the last one is the core issue, but I can't figure out how to pass
the binding properly. I don't know why does concept_interface show up as
the first argument.

Thanks,
Benedek