ffc team mailing list archive

[Johan Jansson <johanjan@xxxxxxxxxxxxxxxx>]

On Sun, Sep 11, 2005 at 07:49:35AM -0500, Anders Logg wrote:
> The reason it's a reference is that in a time-stepping loop, you want
> to be able to give the time step k or time t as an argument to the
> form and have it automatically get updated as you change k and t.
> 
> Maybe one should require that one uses references for the constants,
> that is, the constant must exist in a variable outside of the form, in
> the same way as a Function must exist outside of the form?
> 
> /Anders
> 

Ah right, I'll change it back.

I think the only reason it's a problem is because basic types are
usually passed as copies, not references, and it's very common to
construct them on the stack. Maybe it's enough to just make a class
Constant? Then people would treat it just as a Function, and it could
also be generalized to being tensor-valued etc.

I don't think we can keep it this way. As soon as you construct a form
in a separate function from where you use it, you will run into this
issue. Consider:

LinearForm* L;

init()
{
  real c = 13.7;
  L = new LinearForm(c)
}

solve()
{
  L.assemble(); // Here L->c0 is undefined
}

If it wasn't for valgrind telling me exactly what the problem was, I
would have spent a long time scratching my head on this.

  Johan