| Thread Previous • Date Previous • Date Next • Thread Next |
Anders Logg wrote:
On Mon, Feb 16, 2009 at 09:59:01PM +0100, Martin Sandve Alnæs wrote:On Mon, Feb 16, 2009 at 9:39 PM, Anders Logg <logg@xxxxxxxxx> wrote:On Mon, Feb 16, 2009 at 06:11:41PM +0000, A Navaei wrote:2009/2/16 A Navaei <axnavaei@xxxxxxxxxxxxxx>:2009/2/16 Anders Logg <logg@xxxxxxxxx>:On Mon, Feb 16, 2009 at 05:36:48PM +0000, Garth N. Wells wrote:A Navaei wrote:2009/2/16 Anders Logg <logg@xxxxxxxxx>:On Mon, Feb 16, 2009 at 04:36:21PM +0000, A Navaei wrote:2009/2/15 Anders Logg <logg@xxxxxxxxx>:On Sat, Feb 14, 2009 at 06:44:05PM +0000, Garth N. Wells wrote:A Navaei wrote:[snip]Function should not change the FunctionSpace (that's why FunctionSpace is const). FunctionSpace shouldn't depend on the data and its size should be defined when creating the FunctionSpace.The same applies for FunctionSpace as its member variables are private and the public accessors are read-only which. Consider a sub-class ImageFunctionSpace:FunctionSpace, with a constructor like: ImageFunctionSpace(ImageType *imagePtr) where imagePtr is supposed to initialise FunctionSpace::_mesh using the image size, and then _dofmaps itself is initialised using _mesh. How would you do that considering the restrictions?The FunctionSpace has pointers to the mesh, etc. You just need to create your mesh and pass it to the FunctionSpace constructor. What else you then do with the mesh, etc is up to you.That can be done _outside_ of a sub-class. A sub-class of FunctionSpace doesn't have a control over _mesh of its own parent FunctionSpace. The following example may make this more clear: template <typename TImage> class DolfinImageFunctionSpace : public dolfin::FunctionSpace { public: // just some itk typedefs -- ignore typedef TImage ImageType; typedef typename ImageType::PixelType PixelType; typedef typename ImageType::SizeType SizeType; // .. and some dolfin typedefs -- ignore typedef typename std::tr1::shared_ptr<const dolfin::Mesh> MeshConstPointerType; typedef typename std::tr1::shared_ptr<const dolfin::FiniteElement> ElementConstPointerType; typedef typename std::tr1::shared_ptr<const dolfin::DofMap> DofMapConstPointerType; // the ctor DolfinImageFunctionSpace(ImageType* imageData, MeshConstPointerType mesh, ElementConstPointerType element, DofMapConstPointerType dofmap) : dolfin::FunctionSpace(mesh, element, dofmap) { SizeType imageSize = imageData->GetBufferedRegion().GetSize(); // here, we whish to call some thing like: // _mesh = UnitSquare(imageSize[0], imageSize[1]); // but it's private and the accessor is read-only. }; }This breaks the concept of a function space. A function space is defined in terms of a mesh (and other things). A function space does not define its mesh. It looks to me like the class that you're creating should be called something like DolfinImageProblem, which can create its own Mesh, FunctionSpace and other objects. Garth-AliI think what you need to do is something like this: 1. Create a subclass of Function 2. In the constructor of your Function, call the empty Function() constructor 3. Then, still in the constructor of your Function (not FunctionSpace), create everything necessary like figuring out the mesh, dofmap etc and from that create a FunctionSpace 4. Then use that FunctionSpace (still in the constructor of your Function subclass) to create a new Function v which uses your special FunctionSpace in its constructor 5. Finally, assign this function to the created Function: *this = v;error: no match for 'operator=' in '*(itk::DolfinImageFunction<itk::Image<double, 2u> >*)this = v' Assigning Function to ImageFunction is a trouble, see the full code here: http://code.google.com/p/wrapitk/source/browse/trunk/ExternalProjects/ItkDolfin/src/itkDolfinImageFunction.h#87Do you have the latest hg version? Function assignment should work (see recent discussion on the mailing list on copy constructors and assignment operators for Function).I don't understand the philosophy behind this tight security: why no protected member variables? Why is everything either public or private? Needless to say, the protected members were designed to allow class extensions, by banning it, you're making sub classing a unnecessarily complicated task. The above problem has it's own work arounds, but I don't understand why the obvious way is blocked.The reason is simply that the constructor arguments in Function and FunctionSpace are const. This means no one is allowed to change the variables, not even the Function class (or FunctionSpace class) itself. For example, it's reasonable when you create a Function on a FunctionSpace that the Function will not change the FunctionSpace.Whether the member variables are read-only or not, and their visibility are two separate concepts - you can have any combination of these. Function and FunctionSpace do change their const variables anyway, eg, in operator= you have: // Assign vector init(); dolfin_assert(_vector); *_vector = *v._vector; Which is in contradiction with what you wrote about not even the class itself cannot change the variables.Anders was referring to FunctionSpace. Obviously, the vector associated with a discrete Function cannot be const (and it isn't).It would be rare that all classes have to have read-only inputs, where the sub-classes are setences to inherit the same properties. Now, I simply cannot have the right operator= assinging Function to ImageFunction implemented, since I cannot assign anything to the private member variables. If the visibility of the members variables is not going to change to protected, or at least a protected read/write accessor is not provided, then there will be no option but implementing everything in a third-party class faking the current ImageFunction, as it's not going to be derived from Function.All you need to do is create a suitable FunctionSpace before creating your Function. GarthYes, and you should be able to create that FunctionSpace inside the constructor for your Function subclass.Yes, I can _create_ it, but I cannot _assign_ it :) Now I'm trying this work around: DolfinImageFunction(ImageType* imageData) : dolfin::Function() { ... // Create a Function instance FSConstPointerType V = CreateFunctionSpace(); DolfinImageFunction v(V); *this = v; }; which requires the repsence of this ctor: DolfinImageFunction(boost::shared_ptr<const dolfin::FunctionSpace> V): dolfin::Function(V) { }; This might work.Yes, that's what I suggested (but maybe I didn't explain it too well).The above builds, but then I get thos runtime error: RuntimeError: *** Error: Cannot copy Functions which do not have a Vector (user-defined Functions). The error originates from 'this' instance and not from v. Just in case, here is the full code: http://code.google.com/p/wrapitk/source/browse/trunk/ExternalProjects/ItkDolfin/src/itkDolfinImageFunction.h#47Yes, this is expected and in accordance with another thread today on assignment of Functions. It is not possible to assign Functions which are only defined by an eval() operator (like in your case). The real problem here is that C++ does not allow anything to happen between the call to the contstructor and the initialization of the base class. What you really want to do is this: DolfinImageFunction(ImageType* imageData) { // Create function space FSConstPointerType V = CreateFunctionSpace(imageData); // Initialize base class Function(V); } This is possible in Python but not C++ as the call to the base class constructor must happen before the constructor body. The only solution I see is to add an init() function to Function that allows a user to set the FunctionSpace. Either we name it init() as we've done in many other DOLFIN classes, or we add a function named set_function_space() which would match has_function_space().You still haven't explained why making member variables protected instead of private is not an option, as was asked for? Might be a good reason, but I'm curious too what that reason is.I'd like all member variables to be private unless there's a very good reason not to make them private. The Function/FunctionSpace classes are particularly intricate with a _vector that may or may not be null depending on the current state of the Function, so by allowing access only through public functions we can perform checks (which we could do better) and some magic. For example, calling vector() does not only return the vector instance, it also creates the vector and initializes it with the correct size if necessary.
It also makes it easier for users to develop against evolving versions of DOLFIN. For example, we recently changed the storage in a number of classes from plain pointers to shared pointers which cannot have affected user-created sub-classes since the data is private.
Garth
------------------------------------------------------------------------ _______________________________________________ DOLFIN-dev mailing list DOLFIN-dev@xxxxxxxxxx http://www.fenics.org/mailman/listinfo/dolfin-dev
| Thread Previous • Date Previous • Date Next • Thread Next |
