Question

I have a KillerSudoku class in my application.

Every instance has many cells in @cells, many zones in @zones and so on.

Is there a way to easily copy an object (the sudoku) copying all it’s “sub-objects”, that’s to say, I want my copy to have cells and zones I can modify without modifying the previous sudoku?

Answer 1

Assuming that all parts are serializable by Marshal and you want a completely deep clone:

class Object
  # This doesn't have to be on Object; it could be on KillerSudoku instead
  def deep_clone
    Marshal.load(Marshal.dump(self))
  end
end

Seen in action:

class KillerSudoku
  attr_accessor :cells
end

ks1 = KillerSudoku.new
ks1.cells = ["one",2,3]

ks2 = ks1.deep_clone
ks2.cells.pop
ks2.cells.first.reverse!

p ks1.cells, ks2.cells
#=> ["one", 2, 3]
#=> ["eno", 2]           # New array with all instance values being uniq, too

From the docs, the above won’t work if you have any of the following in your structures:

• anonymous Class or Module.

• objects which are related to the system (e.g. Dir, File::Stat, IO, File, Socket, etc.)

• an instance of MatchData, Data, Method, UnboundMethod, Proc, Thread, ThreadGroup, Continuation

• objects which define singleton methods

---

As seen above, this is a truly deep clone, such that even strings become new instances. If you want the arrays of cells and zones to be cloned, but have all values still referencing the same objects, then you want to customize what dup and clone do by using initialize_copy:

class KillerSudoku
  attr_accessor :cells
  def initialize_copy(old)
    self.cells = old.cells.dup
  end
end

Seen in action:

ks1 = KillerSudoku.new
ks1.cells = ["one",2,3]

ks2 = ks1.clone
ks2.cells.pop
ks2.cells.first.reverse!

p ks1.cells, ks2.cells
#=> ["eno", 2, 3]
#=> ["eno", 2]           # New array that references all the same objects