dolfin team mailing list archive

[Ola Skavhaug <skavhaug@xxxxxxxxx>]

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:

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