void setRow(int row, Vector4 arg)

Assigns the row of the matrix arg

Source 

void setRow(int row, Vector4 arg) {
  final argStorage = arg._v4storage;
  _m4storage[index(row, 0)] = argStorage[0];
  _m4storage[index(row, 1)] = argStorage[1];
  _m4storage[index(row, 2)] = argStorage[2];
  _m4storage[index(row, 3)] = argStorage[3];
}