On Monday 11 June 2007 21:41, dan marsden wrote:

Martin Weiser wrote:

...

- const is transitive, i.e. dereferencing an iterator into a const vector yields a reference to a const element and

- transformation algorithms work on const sequences.

Combined, these two imply that an in-place modification of a sequence through a view generated by a transformation algorithm is impossible. While this is perfectly reasonable for transform, it seems quite restrictive for filter or erase. After all, filter_view accepts a non-const input sequence.

This is a known and currently deliberate restriction. We decided to adopt a simple programming model for the transformation algorithms, that their results are immutable, leading to a functional style of programming. For many algorithms this makes most sense, although filter is the key example of one where allowing you to write into the filtered output seems reasonable.

For now we decided that if users needed mutable behaviour, they could use the equivalent views, such as filter_view, as you identified.

We may loosen the above restrictions in future, depending on feedback such as yours about whether the restriction is a regular annoyance.

Thanks for clarifying this. I didn't locate this issue in the documentation, which may easily be my fault, but otherwise I think it would be worth putting this statement onto the transformation algorithms page. Yours Martin -- Dr. Martin Weiser web: www.zib.de/weiser Zuse Institute Berlin mail: weiser@zib.de Numerical Analysis and Modelling pgp key: www.zib.de/weiser/weiser.asc