/// <summary>
/// Swaps the contents of 'target' with 'source' if the buffers are allocated (1),
/// copies the contents of 'source' to 'target' otherwise (2).
/// Groups should be of same TotalLength in case 2.
/// </summary>
public static bool SwapOrCopyContent(MemoryGroup <T> target, MemoryGroup <T> source)
{
if (source is Owned ownedSrc && ownedSrc.Swappable &&
target is Owned ownedTarget && ownedTarget.Swappable)
{
Owned.SwapContents(ownedTarget, ownedSrc);
return(true);
}