I want to use the enumerator as an integter to have quick pair of the corresponding PETSc enum, e.g.
```  
PetscReal PETScVector::getNorm(VectorNormType  nmtype) const
{
    NormType nm_t[] = {NORM_1, NORM_2, NORM_INFINITY};

    PetscReal norm = 0.;
    VecNorm(_v, nm_t[nmtype], &norm);
    return norm;
}
```