Function process

test/anyflow/test_data.cpp:17–21

class MockProcessor : public GraphProcessor {
 public:
  virtual int process() noexcept override {
    ::std::lock_guard<::std::mutex> lock(**option<::std::mutex*>());
    *x.emit() = *a;
    return 0;
  }

  ANYFLOW_INTERFACE(ANYFLOW_DEPEND_DATA(::std::string, a)
                        ANYFLOW_EMIT_DATA(::std::string, x))