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@hb3p8
Created Apr 28, 2016
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C++14 pattern matching
/*
std::string s = "12";
cout << match(s
,[](int& i) { return "int"; }
,[](bool& b) { return "bool"; }
,[](std::string& s) -> auto& { s += " GAV"; return s; }
,[](auto j) { cout << "default one"; return j; }
);
*/
#include <tuple>
template <typename T>
struct FunctionArgs : FunctionArgs<decltype(&T::operator())> {};
template <typename R, typename... Args>
struct FunctionArgsBase{
using args = std::tuple<Args...>;
using arity = std::integral_constant<unsigned, sizeof...(Args)>;
using result = R;
};
template <typename R, typename... Args>
struct FunctionArgs<R(*)(Args...)> : FunctionArgsBase<R, Args...> {};
template <typename R, typename C, typename... Args>
struct FunctionArgs<R(C::*)(Args...)> : FunctionArgsBase<R, Args...> {};
template <typename R, typename C, typename... Args>
struct FunctionArgs<R(C::*)(Args...) const> : FunctionArgsBase<R, Args...> {};
// forward declarations
template<class T, class Case, class ...Cases>
decltype(auto) match(T&& value, const Case& _case, const Cases&... cases);
template<class T, class Case>
decltype(auto) match(T&& value, const Case& _case);
namespace details {
template<class T, class Case, class ...OtherCases>
decltype(auto) match_call(const Case& _case, T&& value, std::true_type, const OtherCases&... other) {
return _case(std::forward<T>(value));
}
template<class T, class Case, class ...OtherCases>
decltype(auto) match_call(const Case& _case, T&& value, std::false_type, const OtherCases&... other) {
return match(std::forward<T>(value), other...);
}
}
template<class T, class Case, class ...Cases>
decltype(auto) match(T&& value, const Case& _case, const Cases&... cases) {
using namespace std;
using args = typename FunctionArgs<Case>::args;
using arg = tuple_element_t<0, args>;
using match = is_same<decay_t<arg>, decay_t<T>>;
return details::match_call(_case, std::forward<T>(value), match{}, cases...);
}
// the last one is default
template<class T, class Case>
decltype(auto) match(T&& value, const Case& _case) {
return _case(std::forward<T>(value));
}
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