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Small template simplifications #401

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Sep 8, 2016
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Small template simplifications #401

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29 changes: 12 additions & 17 deletions include/pybind11/common.h
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Original file line number Diff line number Diff line change
Expand Up @@ -342,22 +342,24 @@ constexpr size_t constexpr_sum() { return 0; }
template <typename T, typename... Ts>
constexpr size_t constexpr_sum(T n, Ts... ns) { return size_t{n} + constexpr_sum(ns...); }

/// Return true if all/any Ts satify Predicate<T>
// Counts the number of types in the template parameter pack matching the predicate
#if !defined(_MSC_VER)
template <template<typename> class Predicate, typename... Ts>
using all_of_t = bool_constant<(constexpr_sum(Predicate<Ts>::value...) == sizeof...(Ts))>;
template <template<typename> class Predicate, typename... Ts>
using any_of_t = bool_constant<(constexpr_sum(Predicate<Ts>::value...) > 0)>;
using count_t = std::integral_constant<size_t, constexpr_sum(Predicate<Ts>::value...)>;
#else
// MSVC workaround (2015 Update 3 has issues with some member type aliases and constexpr)
template <template<typename> class P, typename...> struct all_of_t : std::true_type { };
template <template<typename> class P, typename T, typename... Ts>
struct all_of_t<P, T, Ts...> : conditional_t<P<T>::value, all_of_t<P, Ts...>, std::false_type> { };
template <template<typename> class P, typename...> struct any_of_t : std::false_type { };
template <template<typename> class P, typename T, typename... Ts>
struct any_of_t<P, T, Ts...> : conditional_t<P<T>::value, std::true_type, any_of_t<P, Ts...>> { };
template <template<typename> class Predicate, typename... Ts> struct count_t;
template <template<typename> class Predicate> struct count_t<Predicate> : std::integral_constant<size_t, 0> {};
template <template<typename> class Predicate, class T, class... Ts>
struct count_t<Predicate, T, Ts...> : std::integral_constant<size_t, Predicate<T>::value + count_t<Predicate, Ts...>::value> {};
#endif

/// Return true if all/any Ts satify Predicate<T>
template <template<typename> class Predicate, typename... Ts>
using all_of_t = bool_constant<(count_t<Predicate, Ts...>::value == sizeof...(Ts))>;
template <template<typename> class Predicate, typename... Ts>
using any_of_t = bool_constant<(count_t<Predicate, Ts...>::value > 0)>;

// Extracts the first type from the template parameter pack matching the predicate, or Default if none match.
template <template<class> class Predicate, class Default, class... Ts> struct first_of;
template <template<class> class Predicate, class Default> struct first_of<Predicate, Default> {
Expand All @@ -373,13 +375,6 @@ struct first_of<Predicate, Default, T, Ts...> {
};
template <template<class> class Predicate, class Default, class... T> using first_of_t = typename first_of<Predicate, Default, T...>::type;

// Counts the number of types in the template parameter pack matching the predicate
template <template<typename> class Predicate, typename... Ts> struct count_t;
template <template<typename> class Predicate> struct count_t<Predicate> : std::integral_constant<size_t, 0> {};
template <template<typename> class Predicate, class T, class... Ts>
struct count_t<Predicate, T, Ts...> : std::integral_constant<size_t,
Predicate<T>::value + count_t<Predicate, Ts...>::value> {};

/// Defer the evaluation of type T until types Us are instantiated
template <typename T, typename... /*Us*/> struct deferred_type { using type = T; };
template <typename T, typename... Us> using deferred_t = typename deferred_type<T, Us...>::type;
Expand Down