How can we convert the requirements In this question link to a concept
I have attempted the following:
template< typename U, typename Tin, typename Tout>
concept MyConditions =
(
U::value_type
&& Tin::value_type
&& Tout::value_type
&& std::is_floating_point_v<typename Tin::value_type>
&& std::is_integral_v<typename U::value_type>
&& std::is_floating_point_v<typename Tout::value_type>
);
This concept is now applied to one of my member functions:
class test_concept
{
template< typename U, typename Tin, typename Tout>
requires MyConditions <U, Tin, Tout>
static void test_routine(const U&, const Tin&, Tout& );
}
When testing:
std::vector<double> test{ };
std::vector<int> testi{ };
std::vector<double> test2{ };
test_concept::test_routine(testi, test, test2);
Using clang
I get the error message that no matching were found, and a note saying:
note: because substituted constraint expression is ill-formed: missing 'typename' prior to dependent type name 'vector<int, allocator >::value_type' U::value_type
You don't need to manually check for the presence of the types. If they're not there, SFINAE will cause your concept to silently return false
anyway. So:
template< typename U, typename Tin, typename Tout>
concept MyConditions =
std::is_integral_v<typename T::value_type> &&
std::is_floating_point_v<typename U::value_type> &&
std::is_floating_point_v<typename Tout::value_type>;
But if you want to explicitly check for the types, here's the syntax:
template< typename U, typename Tin, typename Tout>
concept MyConditions =
requires
{
typename U::value_type;
typename Tin::value_type;
typename Tout::value_type;
} &&
std::is_integral_v<typename T::value_type> &&
std::is_floating_point_v<typename U::value_type> &&
std::is_floating_point_v<typename Tout::value_type>;
You can also move all conditions into the requires
:
template< typename U, typename Tin, typename Tout>
concept MyConditions =
requires
{
typename U::value_type;
typename Tin::value_type;
typename Tout::value_type;
requires std::is_integral_v<typename T::value_type>;
requires std::is_floating_point_v<typename U::value_type>;
requires std::is_floating_point_v<typename Tout::value_type>;
};
Also you should prefer the standard concepts to the old traits:
template< typename U, typename Tin, typename Tout>
concept MyConditions =
requires
{
typename U::value_type;
typename Tin::value_type;
typename Tout::value_type;
requires std::integral<typename T::value_type>;
requires std::floating_point<typename U::value_type>;
requires std::floating_point<typename Tout::value_type>;
};
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