Hoi Maarten :-) Maarten Nieber wrote:

Recently I found out that the ublas matrix uses T& when creating a reference to a matrix element. This causes a problem for me, as I'm developing an ublas matrix that has its data on disk rather than in memory:

ublas::matrix< double, row_major, DiskStorage > m; // stores data on disk

I would like ublas::matrix to use the reference type that is declared by its storage type.

typedef A::reference reference;

So you would like to replace the following two lines in matrix.hpp (within the definition of boost::matrix): typedef const T &const_reference; typedef T &reference; By the following: typedef typename A::const_reference const_reference; typedef typename A::reference reference; Right? (Mind the typename!) And in your case, A is your DiskStorage class.

My question is: is this a mistake in the design, or is there a reason why T& should always be the reference type of an ublas matrix?

When you locally make the changes to your copy of matrix.hpp, does it all work for you? I don't have an answer to your question, I just hope that it will get some more attention...

As an illustration, here is some code using the reference type of the DiskStorage class:

DiskStorage aDiskStorage( 100 ); // create a disk storage with 100 elements DiskStorage::reference r = aDiskStorage[0]; r = 123.456; // writes 123.456 to disk

Cool. :-) Kind regards, -- Niels Dekker http://www.xs4all.nl/~nd/dekkerware Scientific programmer at LKEB, Leiden University Medical Center