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C ++ 1z - 检查是否在可变参数模板参数包中传递了类型

更新时间:2023-08-25 10:16:16

您正在查找 std :: disjunction 。它在 N4564 中指定 [meta.logical]

You're looking for std::disjunction. It's specified in N4564 [meta.logical].

#include <type_traits>

template<typename T, typename... Ts>
constexpr bool contains()
{ return std::disjunction_v<std::is_same<T, Ts>...>; }

static_assert(    contains<int,      bool, char, int, long>());
static_assert(    contains<bool,     bool, char, int, long>());
static_assert(    contains<long,     bool, char, int, long>());
static_assert(not contains<unsigned, bool, char, int, long>());

Live演示

或适用于 struct

template<typename T, typename... Ts>
struct contains : std::disjunction<std::is_same<T, Ts>...>
{};






或使用折叠表达式


Or, using fold expressions

template<typename T, typename... Ts>
struct contains : std::bool_constant<(std::is_same<T, Ts>{} || ...)>
{};

Live演示