meta::range

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

template <typename T>
concept range =
  requires(T&& t) {
    /* using std::begin; */ begin(t);
    /* using std::end; */ end(t);
  };

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

---

Differences with the C++20 version

• The implementation does not rely on std::ranges::begin, but on the usual customization point idiom, i.e. using std::begin; begin(/* ... */);.

Concept emulation

namespace mgs {
namespace meta {

template <typename T>
struct is_range { /* ... */ };

template <typename T>
constexpr auto is_range_v = is_range<T>::value;

template <typename T,
          typename = std::enable_if_t<is_range_v<T>>>
using range = T;

} // namespace meta
} // namespace mgs

Example

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

using namespace mgs::meta;

struct output_range {
  std::back_insert_iterator<std::string> begin();
  std::back_insert_iterator<std::string> end();
};

static_assert(is_range_v<std::string>, "");
static_assert(is_range_v<char [2]>, "");
static_assert(is_range_v<output_range>, "");