Copy for BigObjects not working

[saschatimme]

Consider this code

P=Polymake.polytope.cube(3)
Q=copy(P)

type: Polytope<Rational>
description: cube of dimension 3

AFFINE_HULL
	

BOUNDED
	true

CONE_AMBIENT_DIM
	4

CONE_DIM
	4

FACETS
  1   1   0   0
  1  -1   0   0
  1   0   1   0
  1   0  -1   0
  1   0   0   1
  1   0   0  -1

VERTICES_IN_FACETS
	{0 2 4 6}
	{1 3 5 7}
	{0 1 4 5}
	{2 3 6 7}
	{0 1 2 3}
	{4 5 6 7}

P.VERTICES
Q

type: Polytope<Rational>
description: cube of dimension 3

AFFINE_HULL
	

BOUNDED
	true

CONE_AMBIENT_DIM
	4

CONE_DIM
	4

FACETS
  1   1   0   0
  1  -1   0   0
  1   0   1   0
  1   0  -1   0
  1   0   0   1
  1   0   0  -1

FEASIBLE
	true

LINEALITY_SPACE
	

N_FACETS
	6

N_VERTICES
	8

POINTED
	true

VERTICES
  1  -1  -1  -1
  1   1  -1  -1
  1  -1   1  -1
  1   1   1  -1
  1  -1  -1   1
  1   1  -1   1
  1  -1   1   1
  1   1   1   1

VERTICES_IN_FACETS
	{0 2 4 6}
	{1 3 5 7}
	{0 1 4 5}
	{2 3 6 7}
	{0 1 2 3}
	{4 5 6 7}

The P.VERTICES triggers the computation of the vertices also in Q. So we definitely didn't create a proper copy. deepcopy also doesn't work.
Some research

julia> @which copy(P)
copy(arg1::Union{CxxWrap.CxxWrapCore.ConstCxxRef{var"#s36"} where var"#s36"<:Polymake.BigObject, CxxWrap.CxxWrapCore.CxxRef{var"#s35"} where var"#s35"<:Polymake.BigObject, Union{CxxWrap.CxxWrapCore.SmartPointer{T2}, T2} where T2<:Polymake.BigObject}) in Polymake at /Users/sascha/.julia/packages/CxxWrap/OcN1Z/src/CxxWrap.jl:618

One way to get an honest copy is to do:

Q = Polymake.polytope.Polytope(P)

My Polymake foo is not enough to come up with a general solution.

[kalmarek]

I might be wrong, but it's by design: polymake objects try very hard not to be copied ;)

[benlorenz]

I was slightly surprised that Q = Polymake.polytope.Polytope(P) does work, because the default copy constructor for BigObject will not create a copy but just a new reference. But since we use the "type" Polytope (the function name) for the construction using a new BigObjectType we do get a copy in that case. (it uses a BigObject(BigObjectType,BigObject) constructor on the C++ side)

In this case we are even dealing with perl references that also avoid copying.
But there is an easy way to solve this, we can just add a mapping for the following method for BigObject to libpolymake-julia:

class BigObject {
...
   // construct an exact copy (up to temporary properties and local extensions)
   BigObject copy() const;

I'm not totally sure what julia function we should map that to (copy, deepcopy, deepcopy_internal,...) ?