Method interface

common/values/opaque_value.h:279–284

  }

  const OpaqueValueInterface* absl_nullable interface() const {
    if (dispatcher_ == nullptr) {
      return content_.To<OpaqueValueInterface::Content>().interface;
    }
    return nullptr;
  }

  friend void swap(OpaqueValue& lhs, OpaqueValue& rhs) noexcept {
    using std::swap;