On 01/09/2014 11:04 PM, Peter Alexander wrote:
Trying to write a bit more about D on my blog now. To start, I've
written about a proof-of-concept range-based API for graph search.


I'd greatly appreciate any feedback on the design.

I like the general direction.

One issue with the API is that it does not deal with graphs with more than one edge between two given vertices very well. I think it'd need a separate edge abstraction. (Formally, a graph is just a pair of sets (V,E) with two functions from E to V giving you start and end vertex of an edge.)

A graph search can have more properties than just the sequence of visited edges, so maybe it is not a range, but just provides a range. (And maybe also a range of events, usable instead of callbacks, maybe a DFS tree etc.)

Allocation of memory for visited flags and the like should be controllable. Maybe the design should even allow using persistent data structures for storing visited flags, such that the search range can be used as a value type / forward range.

As we don't yet have
a graph library for D, it would be interesting to discuss APIs in general.


Probably it would be worthwhile to explore a design that is similar to Phobos ranges at some level. I.e. support kinds of graphs with different capabilities. (Eg. your implicitGraph cannot enumerate all vertices or edges that are present in the Graph. The least capable graph kind reasonably supported might not even be able to quickly report all adjacent edges to a vertex. Some graphs may allow in-place mutation etc.) Then provide some explicit representations with high capabilities and helper functions to convert certain representations to (more) explicit representations. (similar to constructing eg. an array from a range.) Constructions on graphs would then return implicit representations.

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