When using Types or Matrix with the nvcc compiler with Wunused-value
enabled you would get the following warning:
(__builtin_expect(!(rowIndex < (this,NUM_ROWS)), 0)) ?
__assert_rtn(__func__, "vtkm/Matrix.h", 86, "rowIndex < this->NUM_ROWS") :
((void)0);

This is solved by changing this->NUM_ROWS to just NUM_ROWS.