Question

I would like to have a C++ class that gets initialized from a file that contains a bunch of data, reads the data, and stores it as const data members.

What I currently do is

MyClass(const std::string & fileName):
datum0(),
datum1(),
datum2()
{
  this->read(fileName);
  // read() sets all datumX data members.
}

This has the disadvantage that the datumXs cannot be marked const anymore since they are set up after the actual initialization step.

What would be a good pattern here?

Answer 1

Instead of set of datumX members – use struct with these members which have constructor from file. And make this struct const data member of your class:

class MyClass {
   ...
   struct MyData {
     MyData(const string& filename) { read(filename); }
     void read(const string& filename);
     int datum1;
     int datum2;
     ...
   };
   const MyData myData;
   MyClass(const string& filename) : myData(filename) {}
};