dolfin team mailing list archive

["Garth N. Wells" <gnw20@xxxxxxxxx>]

On 25 February 2013 08:45, Martin Sandve Alnæs <martinal@xxxxxxxxx> wrote:
> Sounds confusing to me.

I'm confused. Is it a hack to get around a design flaw further up the chain?

Does it have to be a constructor? What's wrong with
> a shallow_copy() function?
>

No need for that either because one can already access shared pointers
to the function space and vector.

I like to avoid shallow copies. It gets confusing as objects have more
data and increases the likelihood that a code change will have
knock-on effects.

Garth

> Martin
>
>
> On 22 February 2013 14:25, Johan Hake <hake.dev@xxxxxxxxx> wrote:
>>
>> On 02/22/2013 02:18 PM, Garth N. Wells wrote:
>> > On 22 February 2013 13:13, Johan Hake <hake.dev@xxxxxxxxx> wrote:
>> >> Any comment on this?
>> >>
>> >> Basically we need another constructor which generates a shallow copy of
>> >> a Function, which also has access to the original Function.
>> >>
>> >
>> > Would this be a non-issue if using a shared_ptr? What's the difference
>> > between a shallow copy of a Function and a pointer to a Function?
>>
>> The shared_ptr is just a way to differ a deep copy from a shallow copy.
>> Using a shared_ptr is really just an abuse of syntax. The shared_ptr
>> will not be passed to the new Function anyhow. There might be other ways
>> to differentiate these two constructors from each others. The obvious
>> being:
>>
>>   Function(const Function& other, bool deepcopy)
>>
>> but not sure that is any better...
>>
>> The reason we need this in the first place is to be able to generate a
>> Python wrapped version of a Function when such is returned from the C++
>> interface. With a shallow copy constructor we minimize the amount of
>> copying.
>>
>> Johan
>>
>> > Garth
>> >
>> >> Johan
>> >>
>> >> On 02/21/2013 07:08 PM, Johan Hake wrote:
>> >>> Hello!
>> >>>
>> >>> To fix:
>> >>>
>> >>> [child().child() fails for Function and FunctionSpaces in Python]
>> >>> https://bugs.launchpad.net/bugs/1130354
>> >>>
>> >>> we need to add a way of shallow copy a Function. For now we have used:
>> >>>
>> >>> Function(boost::shared_ptr<const FunctionSpace> V,
>> >>>          boost::shared_ptr<GenericVector> x);
>> >>>
>> >>> Which create a new Function with a shared FunctionSpace and
>> >>> GenericVector. The problem is that there is no way of bringing
>> >>> Hierarchical data to the new Function as it is not passed through the
>> >>> constructor.
>> >>>
>> >>> We would need something like:
>> >>>
>> >>> Function(boost::shared_ptr<const Function> u);
>> >>>
>> >>> which is interpreted as a shallow copy.
>> >>>
>> >>> We could then map this to:
>> >>>
>> >>>   Function._shallow_copy()
>> >>>
>> >>> and
>> >>>
>> >>>   Function(const Function& u);
>> >>>
>> >>> to
>> >>>
>> >>>   Function._deep_copy()
>> >>>
>> >>> in the Python interface. Then we add:
>> >>>
>> >>>   Function.
>> >>>
>> >>>   def copy(self, deepcopy=True):
>> >>>      if deepcopy:
>> >>>         return self._deep_copy()
>> >>>      else:
>> >>>         return self._shallow_copy()
>> >>>
>> >>> Any objections to adding:
>> >>>
>> >>>   Function(boost::shared_ptr<const Function> u);
>> >>>
>> >>> as a shallow copy constructor?
>> >>>
>> >>> If so we could maybe remove:
>> >>>
>> >>>    Function(boost::shared_ptr<const FunctionSpace> V,
>> >>>             boost::shared_ptr<GenericVector> x);
>> >>>
>> >>> as I think we added it so we could create a shallow copy in the Python
>> >>> interface.
>> >>>
>> >>> Johan
>> >>>
>> >>
>> >>
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>