copy with matrix argument gives error

[matthias314]

The following code works for AbstractAlgebra, but not for Nemo (v0.32.2):

julia> a = zero_matrix(ZZ, 2, 2);
julia> copy(a)
ERROR: MethodError: no method matching copy(::fmpz_mat)

The same happens with QQ and GF(2) instead of ZZ. Shouldn't Nemo provide a method for copy?

[thofma]

It is impossible to define a copy method for Nemo matrices with the same semantics. We should probably remove the copy method in AbstractAlgebra to make it more uniform.

[matthias314]

Maybe the exact semantics are impossible. But it must be possible to produce a matrix B that is equal to a given matrix A and that one can modify without changing A. I think there are use cases for such a function, and it would make sense to call it copy.

[thofma]

There is deepcopy.

[matthias314]

Yes. Instead of removing copy from AbstractAlgebra, would it make sense to make it call deepcopy in Nemo? Plain Julia also provides copy for arrays, so people might expect it to exist for other matrix types. I would guess that most users are not concerned about the exact semantics, but only want a cheap way to get a copy.