constructor helper

 template<class T>
  class Foo : public generalFoo<T> {
  public:

    Foo(const int& size = 3,
                  const double& variance = -1.0);

    void generate(const int& size,
                  const double& theVariance=-1.0);

    const double& getActualVariance() const;
  protected:
    double variance;
  };

  template<class T>
    Foo<T>::Foo(const int& size,
                                    const double& theVariance)
    : generalFoo<T>() {

    generate(size,theVariance);
  }

  // generate filter
  template<class T>
    void  Foo<T>::generate(const int& size,
                                     const double& theVariance) {

    // do something here.
  }

  template<class T>
  const double& gaussKernel1D<T>::getActualVariance() const {
    return variance;
  }