meta::assignable_from¶

Defined in header <mgs/meta/concepts/assignable_from.hpp>.

template <typename LHS, typename RHS>
concept assignable_from =
  std::is_lvalue_reference_v<LHS> &&
  meta::common_reference_with<
    std::remove_reference_t<LHS> const&,
    std::remove_reference_t<RHS> const&> &&
  requires(LHS lhs, RHS&& rhs) {
    lhs = std::forward<RHS>(rhs);
    requires meta::same_as<decltype(lhs = std::forward<RHS>(rhs)), LHS>;
  };

Pre-C++20 implementation of the std::assignable_from concept.

Concept emulation¶

namespace mgs {
namespace meta {

template <typename LHS, typename RHS>
struct is_assignable_from { /* ... */ };

template <typename LHS, typename RHS>
constexpr auto is_assignable_from_v = is_assignable_from<LHS, RHS>::value;

template <typename LHS, typename RHS,
          typename = std::enable_if_t<is_assignable_from_v<LHS, RHS>>>
using assignable_from = LHS;

} // namespace meta
} // namespace mgs

Example¶

#include <mgs/meta/concepts/assignable_from.hpp>

using namespace mgs::meta;

static_assert(is_assignable_from_v<int&, int const&>, "");
static_assert(!is_assignable_from_v<int&, std::string>, "");

See also¶