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#include <utility>
#include <iterator>
#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <unordered_map>
#include <string>
#include <memory>
#include <type_traits>
#include <functional>
#include <regex>
#include <boost/variant.hpp>
template<class F>
struct pseudo_method {
F f;
// enable C++17 class type deduction:
pseudo_method( F&& fin ):f(std::move(fin)) {}
// Koenig lookup operator->*, as this is a pseudo-method it is appropriate:
template<class Variant> // maybe add SFINAE test that LHS is actually a variant.
friend decltype(auto) operator->*( Variant&& var, pseudo_method const& method ) {
// var->*method returns a lambda that perfect forwards a function call,
// behaving like a method pointer basically:
return [&](auto&&...args)->decltype(auto) {
// use visit to get the type of the variant:
return boost::apply_visitor(
[&](auto&& self)->decltype(auto) {
// decltype(x)(x) is perfect forwarding in a lambda:
return method.f( decltype(self)(self), decltype(args)(args)... );
},
std::forward<Variant>(var)
);
};
}
};
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clang++ --version
clang++ -std=c++1z -O2 -Wall -pedantic -pthread main.cpp && ./a.out

clang version 3.8.0 (tags/RELEASE_380/final 263969)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/local/bin
AB