Ticket #11015: bgl_csr_edge_hash_fix.h

#pragma once

#include <cstddef>
#include <type_traits>
#include <limits>


// Specializing hash<> for user-defined type in std namespace, this is standard conforming.
namespace std {

template <typename Vertex, typename EdgeIndex>
struct hash<boost::detail::csr_edge_descriptor<Vertex, EdgeIndex>> {
  std::size_t operator()(const boost::detail::csr_edge_descriptor<Vertex, EdgeIndex>& edge_descriptor) const noexcept {

    static_assert(std::is_unsigned<EdgeIndex>(),
                  "An unsigned EdgeIndex is required for simple hashing returning the edge descriptor's index");
    static_assert(std::numeric_limits<EdgeIndex>::max() <= std::numeric_limits<std::size_t>::max(),
                  "EdgeIndex too large for simple hashing returning the edge descriptor's index");

    return edge_descriptor.idx;
  }
};
}