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Use C++17 fold expression macro

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This puts the fold expressions behind the feature macro instead of a
general C++17 macro.

It also adds a fold expression optimization to constexpr_sum (guarded
by the same feature macro).
This commit is contained in:
Jason Rhinelander 2017-03-17 00:41:09 -03:00
parent efa8726ff7
commit d51acb6873
1 changed files with 5 additions and 1 deletions
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6
include/pybind11/common.h
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@ -401,7 +401,7 @@ template <bool B> using bool_constant = std::integral_constant<bool, B>;
template <typename T> struct negation : bool_constant<!T::value> { };
/// Compile-time all/any/none of that check the boolean value of all template types
#ifdef PYBIND11_CPP17
#ifdef __cpp_fold_expressions
template <class... Ts> using all_of = bool_constant<(Ts::value && ...)>;
template <class... Ts> using any_of = bool_constant<(Ts::value || ...)>;
#elif !defined(_MSC_VER)
@ -444,9 +444,13 @@ struct void_type { };
template <typename...> struct type_list { };
/// Compile-time integer sum
#ifdef __cpp_fold_expressions
template <typename... Ts> constexpr size_t constexpr_sum(Ts... ns) { return (0 + ... + size_t{ns}); }
#else
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...); }
#endif
NAMESPACE_BEGIN(constexpr_impl)
/// Implementation details for constexpr functions