CODEWITHSUNDEEP
c++
Bronze
Bronze

Reputation: 143

Why does std::bind not adapt function signatures?

I'm about to tear my hair out. I don't know if I'm doing something wrong or fundamentally misunderstanding what std::bind is for. I am calling this function:

void fetch(Face& face,
           const Interest& baseInterest,
           shared_ptr<Validator> validator,
           const CompleteCallback& completeCallback,
           const ErrorCallback& errorCallback);

like this:

ndn::util::SegmentFetcher::fetch(
  m_nlsrFace,
  interest,
  m_validator,
  [&datasetBlob](const ndn::ConstBufferPtr& data){
    datasetBlob = data;
  },
  std::bind(&Nlsr::onFaceDatasetFetchTimeout,
            _1, _2, datasetBlob, interest));

And the signature for ErrorCallback is like this:

typedef function<void (uint32_t code, const std::string& msg)> ErrorCallback;

The error that is being thrown at me is this:

/usr/local/include/ndn-cxx/util/segment-fetcher.hpp:141:3: note:
  no known conversion for argument 5 from ‘
    std::_Bind_helper<
      false,
      void (nlsr::Nlsr::*)(unsigned int,
                           const std::basic_string<char>&,
                           const std::shared_ptr<const ndn::Buffer>&,
                           ndn::Interest),
      const std::_Placeholder<1>&,
      const std::_Placeholder<2>&,
      std::shared_ptr<const ndn::Buffer>&,
      ndn::Interest&>::type
  {aka std::_Bind<std::_Mem_fn<void (nlsr::Nlsr::*)(
                                 unsigned int,
                                 const std::basic_string<char>&,
                                 const std::shared_ptr<const ndn::Buffer>&,
                                 ndn::Interest)>
                    (std::_Placeholder<1>,
                     std::_Placeholder<2>,
                     std::shared_ptr<const ndn::Buffer>,
                     ndn::Interest)>}’
  to ‘const ErrorCallback&
  {aka const std::function<void(unsigned int, const std::basic_string<char>&)>&}’

I just don't understand what the issue is. I am binding the function to have the right number of parameters (and of the right type, too!) and fixing the others. But it seems that std::bind doesn't change the function signature, because I appear to be having issues with type resolution. What then is the use of std::bind? I am using it incorrectly?

Upvotes: 0

Views: 300

Answers (1)

Jarod42
Jarod42

Reputation: 217255

As Nlsr::onFaceDatasetFetchTimeout is non static, you have to bind the instance of Nlsr to it (at first argument).

std::bind(&Nlsr::onFaceDatasetFetchTimeout,
          myNlsrObject,
          _1, _2, datasetBlob, interest)

Upvotes: 3

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