array-ops.lua

function DeleteArrayElements( array, index, count ) 
  -- Deletes one or more (count) array elements from the specified index. 
  -- Returns an undo function, which if called would revert the operation.
  
  local deletedElements = {}
  
  assert( index >= 1 and index <= #array, "index=" .. index .. " must be >= 1 and <= " .. #array .. " (#array)" )
  assert( count >= 1 and count <= #array - index + 1, "count=" .. count .. " must be >= 1 and <= " .. #array - index + 1 .. " (#array - index + 1) where #array=" .. #array .. " and index=" .. index)
  
  for i = 0, count - 1 do
    deletedElements[ #deletedElements + 1 ] = array[ index + i ]
  end
  
  for i = 0, #array - index - count do -- move the elements up
    array[ index + i ] = array[ index + count + i ]
  end

  for i = 1, count do -- shrink the array
    array[ #array ] = nil
  end

  return function()
    InsertArrayElements( array, index, deletedElements )
  end
end

function InsertArrayElements( array, index, elements ) 
   -- Inserts, or appends (if index == #array + 1), one or more elements to the array from the specified index. 
   -- Returns an undo function, which if called would revert the operation.
   
   local count = #elements
   
   assert( index >= 1 and index <= #array + 1, "index=" .. index .. " must be >= 1 and <= " .. #array .. " (#array + 1)" )
   assert( count >= 1, "#elements=" .. count .. " must be >= 1" )

   if index <= #array then 
     for i = 1, count do -- extend the array
       array[ #array + 1 ] = ""
     end

     for i = #array, index + count, -1 do -- move the elements down
       array[ i ] = array[ i - count ]
     end
   end
   
   for i = 1, count do -- copy the elements
     array[ index + (i - 1) ] = elements[ i ]
   end
   
   return function() -- Undo Operation
     DeleteArrayElements( array, index, count )
   end
end

function TestInsertDeleteArrayElements()
  local a1 = { 1, 2, 3, 4, "Five", { 1, 2 }, 3 }
  local undo = {}
  
  for i=1,#a1 do print(a1[i]) end
  undo = DeleteArrayElements(a1, 2, 5)
  print("\nAfter Delete:")
  for i=1,#a1 do print(a1[i]) end
  undo(); print("\nUndo:")
  for i=1,#a1 do print(a1[i]) end
  undo = InsertArrayElements(a1, 2, { "Du Du", 3.14, "Samba Di Generio" })
  print("\nAfter Insert:")
  for i=1,#a1 do print(a1[i]) end
  undo(); print("\nUndo:")
  for i=1,#a1 do print(a1[i]) end
end

TestInsertDeleteArrayElements()