As a first step towards a gradual rework of our function metaprogramming helpers,
this change prepends a generic case for all kinds of functors to our existing
solution, which up to now was entirely based on explicit specialisations.
C++11 supplied the new language construct 'decltype(EXPR)', which allows us
to capture any class with an function operator, which also includes the Lambdas.
The solution was proposed 2011 on StackOverflow
http://stackoverflow.com/questions/7943525/is-it-possible-to-figure-out-the-parameter-type-and-return-type-of-a-lambda/7943765#7943765
We used it already with success within our TreeMutator.
But obviously the goal should be to unite all the function trait / metaprogramming helpers,
which unfortunately is a more expensive undertaking, since it also involves
to get rid of the explicit specialisations and retrofit our Types<XXX...> helper
to rely on variadic templates rather than on loki-style typelists.
This first step here is rather conservative, since we'll still rely on our
explicit specialisations in most cases. Only the Lambdas will go through the
new, generic case, and from there invoke the specialisation for member functions.
The latter need to be rectified as well, which is subject of the next changeset...
allow to pick the bare function signature from any "function like" entity
Note: we're still unsing our own Typelist construct to represent
the function argument types. Since we're now using C++11, this
could be replaced by varargs, and we could get rid of those
various overloads for different numbers of arguments.
Unfortunately this transition is linked to the usage of
argument tuples in our command framework (which could then be
replaced by std::tuple), and this is still a bit of rather
technical work, which I do not want to spend much time on
right now
the template _Fun started as an internal helper
for function-closure, but seems to be of
general use. Thus move it into meta/function.hpp
(function-closure.hpp is heavyweight)
