Function GetEnv

getting-started/update/update_gcs_index.cc:31–38

namespace spanner = ::google::cloud::spanner;

std::string GetEnv(char const* var) {
  auto const* value = std::getenv(var);
  if (value == nullptr) {
    throw std::runtime_error("Environment variable " + std::string(var) +
                             " is not set");
  }
  return value;
}

using GetField = std::function<spanner::Value(nlohmann::json const&)>;