dolfin team mailing list archive

[Martin Sandve Alnæs <martinal@xxxxxxxxx>]

On Sat, Feb 14, 2009 at 6:08 PM, Johan Hake <hake@xxxxxxxxx> wrote:
> On Saturday 14 February 2009 17:45:44 Martin Sandve Alnæs wrote:
>> On Sat, Feb 14, 2009 at 5:34 PM, Johan Hake <hake@xxxxxxxxx> wrote:
>> > On Saturday 14 February 2009 17:28:18 Garth N. Wells wrote:
>> >> Johan Hake wrote:
>> >> > On Saturday 14 February 2009 13:48:05 A Navaei wrote:
>> >> >> It seems that the error can be re-produced even without sub-classing
>> >> >> and using existing dolfin classes in pure c++. Based on the
>> >> >> itk-dolfin interface code, the below minimal code should generate the
>> >> >> error (note that I use the binary distribution which uses std::tr1,
>> >> >> replacing it with boost shared pointer should not have any effect).
>> >> >
>> >> > Not in c++ but swig only support std::tr1::shared_ptr from version
>> >> > 1.3.37. But if you intend to use shared_ptr only internally there
>> >> > whould not be any problems.
>> >> >
>> >> >> After wrapping in python:
>> >> >>
>> >> >> (1) Calling FunctionTest.CreateFunction(), which returns by value,
>> >> >> results this error:
>> >> >>
>> >> >> RuntimeError: *** Error: Unable to assign to function, missing
>> >> >> coefficients (user-defined function).
>> >> >
>> >> > You cannot assign another user-defined function to another Function.
>> >> > It must be a discrete function, which has an initialized _vector. This
>> >> > is probably a feature that other developers should answer for.
>> >> >
>> >> > However this means that you cannot copy a userdefined function, with
>> >> > the side effect of not beeing able to return a user-defined Function
>> >> > by value.
>> >> >
>> >> >> Since dolfin::Function does come with the required copy ctors, the
>> >> >> problem cannot be stemmed from this.
>> >> >
>> >> > This use the assignment operator which requires the Function to be a
>> >> > discrete and not a user-defined Function.
>> >> >
>> >> > I consider this to be a bug in the library. Any other comments from
>> >> > the C++ DOLFIN developers (I am mostly dealing with the python
>> >> > interface)?
>> >>
>> >> In a nutshell, are you suggesting that the Function copy constructor
>> >> should work for user-defined Functions?
>> >
>> > Yes. Why shouldn't it?
>> >
>> > I can see why the assigment operator should not work.
>>
>> If I understand this right, what you propose is probably not
>> technically possible in C++ with the current design. The old design
>> which used the envelope-letter could have dealt with this.
>
> Why's that?
>
> The only data that needs to be copied are the FunctionSpace, when _vector is
> null, and this is shared? Am I missing somthing wrt to the copting of any
> derived class of Function?
>
> Johan

I haven't followed this in detail, so I may misunderstand, but if you
have a subclass MyFunction of Function, copying it to a Function can't
possibly work. How could it? However, Function can make a discrete
function from MyFunction, then it's ok.

Martin