static <A, B extends Matrix<A>> B copyMatrix(Matrix<A> src, B dest) {
  assertSameSize(src, dest);
  int w = src.getWidth(), h = src.getHeight();

  for y to h:
    for x to w:
      dest.set(x, y, src.get(x, y));
      
  ret dest;
}

Began life as a copy of #1033649