给定
template <int...> struct Z; template <int...> struct Q;
template <std::size_t...> struct I;
假设我们想要
accumulated_sums<Z<1,2,3,4,5>, Q>::type
成为
Q<1,3,6,10,15>
和
accumulated<I<1,2,3,4,5>, std::integer_sequence>::type
成为
std::index_sequence<1,3,6,10,15>
有没有办法定义 accumulated
通过来自 accumulated_sums
的一些继承方案进行分类类(class)?它们的操作方式完全相同,唯一的区别是模板类型 template <T...> class
对于 accumulated_sums
与略有不同的 template <typename U, U...> class
对于 accumulated
.否则,我必须分别定义这两个类,即使它们的定义本质上是相同的。应该有某种方法可以为两个类定义一次。这是我对这两个类的完全编译代码,您可以看到它们在代码上基本相同。
#include <iostream>
#include <type_traits>
#include <utility>
namespace detail {
template <typename Pack> struct sequence_traits;
template <typename T, template <T...> class Z, T... Is>
struct sequence_traits<Z<Is...>> {
using type = T;
template <T... Js>
using templ_type = Z<Js...>;
};
}
// accumulated_sums
template <typename T, typename Output, template <T...> class, T...> struct accumulated_sums_h;
template <typename T, template <T...> class Z, template <T...> class Q, T Sum, T... Is>
struct accumulated_sums_h<T, Z<Sum, Is...>, Q> {
using type = Q<Is..., Sum>;
};
template <typename T, template <T...> class Z, T Sum, T... Is, template <T...> class Q, T Next, T... Rest>
struct accumulated_sums_h<T, Z<Sum, Is...>, Q, Next, Rest...> :
accumulated_sums_h<T, Z<Sum + Next, Is..., Sum>, Q, Rest...> {};
template <typename Sequence,
template <typename detail::sequence_traits<Sequence>::type...> class = detail::sequence_traits<Sequence>::template templ_type>
struct accumulated_sums;
template <typename T, template <T...> class Z, T First, T... Rest, template <T...> class Q>
struct accumulated_sums<Z<First, Rest...>, Q> :
accumulated_sums_h<T, Z<First>, Q, Rest...> {};
// accumulated
template <typename T, typename Output, template <typename U, U...> class, T...> struct accumulated_h;
template <typename T, template <T...> class Z, template <typename U, U...> class Q, T Sum, T... Is>
struct accumulated_h<T, Z<Sum, Is...>, Q> {
using type = Q<T, Is..., Sum>;
};
template <typename T, template <T...> class Z, T Sum, T... Is, template <typename U, U...> class Q, T Next, T... Rest>
struct accumulated_h<T, Z<Sum, Is...>, Q, Next, Rest...> :
accumulated_h<T, Z<Sum + Next, Is..., Sum>, Q, Rest...> {};
template <typename Sequence, template <typename U, U...> class Q> struct accumulated;
template <typename T, template <T...> class Z, T First, T... Rest, template <typename U, U...> class Q>
struct accumulated<Z<First, Rest...>, Q> :
accumulated_h<T, Z<First>, Q, Rest...> {};
// Testing
template <int...> struct Z;
template <int...> struct Q;
template <std::size_t...> struct I;
int main() {
std::cout << std::boolalpha << std::is_same<
accumulated_sums<Z<1,2,3,4,5>, Q>::type,
Q<1,3,6,10,15>
>::value << '\n'; // true
std::cout << std::is_same<
accumulated_sums<Z<1,2,3,4,5>>::type,
Z<1,3,6,10,15>
>::value << '\n'; // true
std::cout << std::is_same<
accumulated<Z<1,2,3,4,5>, std::integer_sequence>::type,
std::integer_sequence<int, 1,3,6,10,15>
>::value << '\n'; // true
std::cout << std::is_same<
accumulated<I<1,2,3,4,5>, std::integer_sequence>::type,
std::index_sequence<1,3,6,10,15>
>::value << '\n'; // true
}
最佳答案
如果您接受通过 Q<>
而不是 Q
和 std::integer_sequence<int>
(或 std::integer_sequence<std::size_t>
)而不是 std::integer_sequence
(因此模板类型而不是模板模板类型)您可以在底部(请参阅以下示例中的 accumulated_h2
)而不是在顶部 fork 案例(有或没有第一类型模板)
所以你可以使用accumulated
对于这两种情况并扔掉accumulated_sum
.
以下是一个完整的工作示例。
#include <type_traits>
#include <utility>
namespace detail
{
template <typename Pack>
struct sequence_traits;
template <typename T, template <T...> class Z, T... Is>
struct sequence_traits<Z<Is...>>
{ using templ_empty = Z<>; };
}
// accumulated
template <typename T, typename, T...>
struct accumulated_h2;
template <typename T, template <typename, T ...> class Q, T ... Ts>
struct accumulated_h2<T, Q<T>, Ts...>
{ using type = Q<T, Ts...>; };
template <typename T, template <T ...> class Q, T ... Ts>
struct accumulated_h2<T, Q<>, Ts...>
{ using type = Q<Ts...>; };
template <typename T, typename, typename, T...>
struct accumulated_h;
template <typename T, template <T...> class Z, typename C, T Sum, T... Is>
struct accumulated_h<T, Z<Sum, Is...>, C>
{ using type = typename accumulated_h2<T, C, Is..., Sum>::type; };
template <typename T, template <T...> class Z, T Sum, T... Is,
typename C, T Next, T... Rest>
struct accumulated_h<T, Z<Sum, Is...>, C, Next, Rest...>
: accumulated_h<T, Z<Sum + Next, Is..., Sum>, C, Rest...>
{ };
template <typename T,
typename = typename detail::sequence_traits<T>::templ_empty>
struct accumulated;
template <typename T, template <T...> class Z, T First,
T... Rest, typename C>
struct accumulated<Z<First, Rest...>, C>
: accumulated_h<T, Z<First>, C, Rest...>
{ };
// Testing
template <int...>
struct Z;
template <int...>
struct Q;
template <std::size_t...>
struct I;
int main ()
{
static_assert(std::is_same<
accumulated<Z<1,2,3,4,5>, Q<>>::type,
Q<1,3,6,10,15>>::value, "!");
static_assert(std::is_same<
accumulated<Z<1,2,3,4,5>>::type,
Z<1,3,6,10,15>>::value, "!");
static_assert(std::is_same<
accumulated<Z<1,2,3,4,5>, std::integer_sequence<int>>::type,
std::integer_sequence<int, 1,3,6,10,15>>::value, "!");
static_assert(std::is_same<
accumulated<I<1,2,3,4,5>, std::integer_sequence<std::size_t>>::type,
std::index_sequence<1,3,6,10,15>>::value, "!");
}
-- 编辑 --
OP 询问
And how to fork the cases so that
accumulated<std::integer_sequence<T, 1,2,3,4,5>>::type
isstd::integer_sequence<T, 1,3,6,10,15>
, whereT
is any integral type?
我看过你的解决方案,我准备了另一个,差别不大:扔掉旧的 Z
,我用 std::integer_sequence
代替了它而不是你的 squeeze
.
以下是我的代码。
#include <type_traits>
#include <utility>
namespace detail
{
template <typename Pack>
struct sequence_traits;
template <typename T, template <typename, T...> class Z, T... Is>
struct sequence_traits<Z<T, Is...>>
{ using templ_empty = Z<T>; };
template <typename T, template <T...> class Z, T... Is>
struct sequence_traits<Z<Is...>>
{ using templ_empty = Z<>; };
}
// accumulated
template <typename T, typename, T...>
struct accumulated_h2;
template <typename T, template <typename, T ...> class Q, T ... Ts>
struct accumulated_h2<T, Q<T>, Ts...>
{ using type = Q<T, Ts...>; };
template <typename T, template <T ...> class Q, T ... Ts>
struct accumulated_h2<T, Q<>, Ts...>
{ using type = Q<Ts...>; };
template <typename T, typename, typename, T...>
struct accumulated_h;
template <typename T, typename C, T Sum, T... Is>
struct accumulated_h<T, std::integer_sequence<T, Sum, Is...>, C>
{ using type = typename accumulated_h2<T, C, Is..., Sum>::type; };
template <typename T, T Sum, T... Is, typename C, T Next, T... Rest>
struct accumulated_h<T, std::integer_sequence<T, Sum, Is...>, C, Next,
Rest...>
: accumulated_h<T, std::integer_sequence<T, Sum + Next, Is..., Sum>,
C, Rest...>
{ };
template <typename T,
typename = typename detail::sequence_traits<T>::templ_empty>
struct accumulated;
template <typename T, template <T...> class Z, T First,
T... Rest, typename C>
struct accumulated<Z<First, Rest...>, C>
: accumulated_h<T, std::integer_sequence<T, First>, C, Rest...>
{ };
template <typename T, template <typename, T...> class Z, T First,
T... Rest, typename C>
struct accumulated<Z<T, First, Rest...>, C>
: accumulated_h<T, std::integer_sequence<T, First>, C, Rest...>
{ };
// Testing
template <int...>
struct Z;
template <int...>
struct Q;
template <std::size_t...>
struct I;
int main ()
{
static_assert(std::is_same<
accumulated<Z<1,2,3,4,5>, Q<>>::type,
Q<1,3,6,10,15>>::value, "!");
static_assert(std::is_same<
accumulated<Z<1,2,3,4,5>>::type,
Z<1,3,6,10,15>>::value, "!");
static_assert(std::is_same<
accumulated<Z<1,2,3,4,5>, std::integer_sequence<int>>::type,
std::integer_sequence<int, 1,3,6,10,15>>::value, "!");
static_assert(std::is_same<
accumulated<I<1,2,3,4,5>, std::integer_sequence<std::size_t>>::type,
std::index_sequence<1,3,6,10,15>>::value, "!");
static_assert(std::is_same<
accumulated<std::index_sequence<1,2,3,4,5>>::type,
std::index_sequence<1,3,6,10,15>>::value);
static_assert(std::is_same<
accumulated<std::index_sequence<1,2,3,4,5>, I<>>::type,
I<1,3,6,10,15>>::value);
}
关于c++ - 模板类型略有变化后继承特征类,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/46798802/