dolfin team mailing list archive

[Dag Lindbo <dag@xxxxxxxxxx>]

Anders Logg wrote:
> On Thu, Jun 19, 2008 at 11:41:52PM +0200, Dag Lindbo wrote:
>> Hello again!
>>
>> Here comes another suggestion about the DOLFIN public interface:
>>
>> Constructing time dependent functions by subclassing from Function and
>> TimeDependent is very very nice. The way u.sync(t) works by storing a
>> pointer to t is also very clever. However, I think it is too clever --
>> most would expect pass-by-value semantics when passing a scalar to a
>> function. A very simple change could make it a lot clearer what's going
>> on: Pass a pointer to t instead of a constant reference. This forces the
>> user to take the address of the scalar, which really shows what's going
>> on. E.g.
>>
>> u.sync(&t)
>>
>> Today I misunderstood the reference nature of sync(t), and wrote code like
>> this:
>>
>> while(t < T){
>>   "compute timestep"
>>   t += dt
>>   sync_bc(t)
>> }
>>
>> void sync_bc(real t){
>>   for "all Dirichlet BCs"
>>      bc.sync(t)  // Pointer to stack memory gets assigned!!!!
>> }
>>
>> :-( Of course, no one would be foolish enough to pass a pointer to stack
>> memory knowingly in such a short lived context.
>>
>> /Dag
> 
> TimeDependent does not seem to be used anywhere in the code so now
> it's just a fancy way of storing the current time. Objects that want
> to store the current time could equally well just add a member
> 
>   real t;
> 
> I suggest we remove TimeDependent for now and add it back later when
> we find any use for it.
> 
> ok?

No! It is really good feature for non-kernel applications.
I think there is a clear benefit for users to have this base class to
standardize things. It is one of only a handful situations where I
really like multiple inheritance!

/Dag

> 
> 
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> DOLFIN-dev mailing list
> DOLFIN-dev@xxxxxxxxxx
> http://www.fenics.org/mailman/listinfo/dolfin-dev