Viewing file:  template-template-parm1.C (1.12 KB) -rw-r--r--
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// PR c++/66937
// { dg-do compile { target c++17_only } }
// { dg-options "-fconcepts" }
#include <tuple>
namespace detail
{
template<typename T, template<typename...> class Sink>
struct copy_tuple_args_impl;
template<typename... Args, template<typename...> class Sink>
struct copy_tuple_args_impl<std::tuple<Args...>, Sink>
{
using type = Sink<Args...>;
};
}
// copy_tuple_args copies the template arguments of a tuple into another template
// copy_tuple_args does not care about constraints whatsoever.
template<typename Tuple, template<typename...> class Sink>
using copy_tuple_args = typename detail::copy_tuple_args_impl<Tuple, Sink>::type;
// A concept of a column
template <typename T>
concept bool Column()
{
return requires()
{
typename T::_name_t;
};
}
// column_list is constrained to Column arguments
template<Column... C>
struct column_list
{
};
// Here are some columns
struct A
{
using _name_t = int;
};
struct B
{
using _name_t = int;
};
int main()
{
using ColumnTuple = std::tuple<A, B>;
using ColumnList = copy_tuple_args<ColumnTuple, column_list>; // This fails, but should not
}
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