dolfin team mailing list archive

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

Ola Skavhaug wrote:
> On Mon, Sep 7, 2009 at 9:21 AM, Ola Skavhaug<skavhaug@xxxxxxxxx> wrote:
> > We've run into problems since only GenericMatrix provides the default
> > argument for norm type. Swig does not like this and omits generating a
> > constructor for the derived types. According to
> > https://www.securecoding.cert.org/confluence/display/cplusplus/OBJ04-CPP.+Prefer+not+to+give+virtual+functions+default+argument+initializers
> > virtual function should not provide default arguments at it tends to
> > "defeat polymorphism":
> >
> >
> > class Thing {
> >  public:
> >    virtual ~Thing();
> >    virtual void doItNTimes( int numTimes = 10 );
> >    virtual void doItThisHigh( double howHigh = 1.0 );
> >    // ...
> > };
> > class MyThing : public Thing {
> >  public:
> >    void doItNTimes( int numTimes );
> >    void doItThisHigh( double howHigh = 2.2 );
> >    // ...
> > };
> >
> > MyThing *mt = new MyThing;
> > Thing *t = mt;
> > t->doItNTimes(); // default of 10
> > mt->doItNTimes();  // compile time error!
> > t->doItThisHigh(); // default of 1.0!
> > mt->doItThisHigh(); // default of 2.2
> >
> >
> > Is this the intended behaviour anyhow?
> >
> > This is the proposed solution:
>
> Ouch, this was another, bad solution actually :)
>
> The proposed solution (from the link above) is roughly like this:
>
> class Base
> {
>    public:
>       void foo(double bar = 1.0) { foo_impl(bar); }
>    protected:
>       virtual void foo_impl(double bar);
> };
>
> class Sub: public Base
> {
>    protected:
>       virtual void foo_impl(double bar);
> };

This is pretty ugly and I know that I'll forget about it within a day or 
two. I suggest abandoning default arguments for norms if that fixes the 
problem. We have a default argument for str(..), but I think that 
PyDOLFIN has its own mechanism for this.

Note that we have a related Blueprint,

    https://blueprints.launchpad.net/dolfin/+spec/default-parameters-cpp

Garth


> Sorry about that...
>
> Ola
>
> > static double const minimumHeight = 1.0;
> > // ...
> > namespace XYZ {
> > class Thing {
> >  public:
> >    virtual ~Thing();
> >    virtual void doItThisHigh( double howHigh = minimumHeight );
> >    // ...
> > };
> > }
> > // ...
> > namespace XYZ {
> > static double const minimumHeight = 2.2;
> > class MyThing : public Thing {
> >  public:
> >    void doItThisHigh( double howHigh = minimumHeight );
> >    // ...
> > };
> > }
> >
> >
> > Resolving this issue also means getting the Python interface back on track.
> >
> > Ola
> >
> >
> > --
> > Ola Skavhaug