Using temporaries results in crash

[Franco Milicchio]

As said in the Q&A without any feedback, if I use a temporary the assembly dies with the following exception:

#!

*** -------------------------------------------------------------------------
*** Error:   Unable to evaluate expression.
*** Reason:  Missing eval() function (must be overloaded).
*** Where:   This error was encountered inside Expression.cpp.
*** Process: unknown
*** 
*** DOLFIN version: 1.5.0
*** Git changeset:  f467b66dcfd821ec20e9f9070c7cef5a991dbc42
*** -------------------------------------------------------------------------

A simple code as this is sufficient to see how it can die:

    dolfin::Constant c(3.1415);
    lhs.C0000 = dolfin::Constant(3.1415); // DIE
    lhs.C0000 = c;                        // LIVE

It seems that coefficient assigners in a form use the address of a given constant reference in operator=. As said in the Q&A, this results in errors even with a DirichletBC.

A workaround is to duplicate everything with local variables, but you know better than me that this is error-prone.

I've attached an example, but I might have misunderstood how I need to use Fenics.

Thanks!

[Prof Garth Wells]

This is fixed in the development version, which requires coefficients attached to forms to be shared pointers.

[Franco Milicchio]

Good to hear! Does this also imply that I cannot use containers to assign coefficients?

[Prof Garth Wells]

You can use containers, as long as the containers hold std::shared_ptrs to the coefficients.

[Anders Logg (Chalmers)]

Removing milestone: 1.7 (automated comment)