Giovanni P. Deretta wrote:
Hi Eric,
Eric Niebler wrote:
[...]
My proposal is to make Fusion algorithms hierarchical, so they can work efficiently with segmented data structures. Rather that using Matt Austern's formulation, I've come up with a much simpler interface based not on segmented iterators, but rather on segmented sequences.
What's wrong with Austern's interface? I've both implemented and used it and found it both simple and powerful. Then again I didn't deal with anything the complexity of fusion.
It's more complicated than it needs to be for the purposes of Fusion. A strightforward translation of Austern's segmented_iterator_traits<> interface into Fusion would require the following new Fusion primitives (which all operate on Fusion iterator): is_segmented segment local segment_begin segment_end These are necessary because the STL algorithm interface deals with iterators. Fusion's algorithms deal with sequences, however. The proposed segmentation interface for Fusion requires only the following primitives (which operate on Fusion sequences): is_segmented segments where segments(seq) returns seq's segments as a sequence of sequences. This makes it vastly simpler to satisfy the requirements for a segmented Fusion sequence. For example, I implemented segmented Fusion sequence support for a Fusion tree data structure both in Austern's interface and the new one. With Austern's interface, it look ~200 lines of code. With the proposed interface, it took ~50. The implementation of the segmented Fusion algorithms gets dramatically simpler, too. -- Eric Niebler Boost Consulting www.boost-consulting.com