Question

i want to write a library for linear program solving. Thereby several solvers such as cplex or gurobi are used. What i already have is an interface for each of them (all containing the same functions wrapping them to solver specific code).

Now I want to have a class ‘LinearProgram’ which can be instantiated e.g. by LinearProgram(“cplex”) which then invokes the cplex solver.

My first idea was to use a super class ‘solver’ which is a base class of all solver interfaces containing the respective functions as virtual declarations. But then I get an abstract class which can not be instantiated.
So in LinearProgram i wanted to have a variable Solver which is instantiated depending on the string given in the constructor.

I’m sure a proper solution is quite obvious, but all I can think about in the moment is not satisfying.

Thanks for your help.

Answer 1

This illustrates what you describe:

class Solver {
...abstract base
};

class SolverFactory {
public:
    Solver* NewSolverWithName(const std::string& pSolverName);
};

class LinearProgram {
public:
    LinearProgram(const std::string& pSolverName) :
      d_solver(SolverFactory::NewSolverWithName(pSolverName)) {
    }
private:
    some_auto_pointer<Solver> d_solver;
};

class cplex_Solver : public Solver {
...
    static std::string Name();
};

Solver* SolverFactory::NewSolverWithName(const std::string& pSolverName) {
    if (pSolverName == cplex_Solver::Name()) {
      return new cplex_Solver();
    }
    ...
}