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Re: [glas] Reference counting?

From: Karl Meerbergen (Karl.Meerbergen_at_[hidden])
Date: 2007-10-16 02:55:54

Pieter Collins wrote:

>I think that a general-purpose package needs to provide vector/matrix
>classes taylored to various uses. An application using many 3d vectors
>will have very different requirements (fast allocation/deallocation,
>efficient storage) to an application using 1000x1000 matrices (efficient
>manipulation using views/slices).
>As I see it, reference counting will improve safety and may allow
>storage and slicing to be implemented by the same class, but does not
>introduce extra mathematical functionality. The expense is probably
>worth it for large objects, but not for small objects.
>Regarding the copy semantics, how about introducing a new concept
>"VectorView" which uses shallow copies to complement "VectorContainer"
>which uses deep copies? It seems like this concept is sufficiently
>important to be worth adding, though I generally think it's important to
>keep the number of different concepts to a minimum.
>Presumably it would be possible to separate storage (including reference
>counting) from the rest of the code by using an array template argument
>similar to uBlas.

Hi Pieter,

At this stage, there is no container concept in GLAS, so all options are
still open. I am in favour of having two container concepts, as you
suggest, View and Container, one with a deep copy constructor, the other
with a shallow copy constructor. I am currently using a shared_ptr for
this instead of a view.

If two types of containers exist, the user has to be aware of the
difference in behaviour between copy constructors.

I am not sure that a template argument is good enough to make clear that
the copy constructor has different behaviour ?!

Currently you can do something like

dense_vector<double> v( 10 ) ;
dense_vector<double> w( 4.0 * v ) ;

This does not make sense with a shallow copy. In the case of a shallow
copy, this could become:

dense_vector<double> v( 10 ) ;
dense_vector<double> w( size(v) ) ; w = 4.0 * v ;

Best regards,