Use Attributes for all mathematical properties (weight, balance etc.)

[clue]

See #103.

[clue]

This ticket will remove all mathematical properties from the Vertex and Edge classes, such as weight, balance etc. and will use general purpose Attributes instead.

This means that all of these will have to be set via attributes in the future:

// old
$edge->setWeight(10.5);

// new
$edge->setAttribute('weight', 10.5);

This has several consequences:

• A big BC break obviously :-)
• Attribute type validation is no longer possible ("weight" could be a string)
• Attribute constraints are no longer possible ("flow" could exceed "capacity")
• Attribute names are not standardized in any way
  • We should probably reserve a "well known namespace" or similar
  • Algorithms classes need a way to set the required attribute names

I'll look into this to see how it works out.

[cyberscribe]

It seems to me that retaining getWeight/setWeight as an interface to the arbitrary attributes in a future version would allow you to retain BC.

While GraphML stores weights as an arbitrary attribute in representation, in practice the weight value is highly significant in that it differentiates a graph from a network. Tools like Gephi respect it as significant and change how they render the graph based on its presence.

So, I think there is a big difference between whether a variable is "special" in terms of how it gets stored or rendered, and whether it is "special" in terms of how it gets used. To my mind, weight is "special" in practice, and so retaining getters/setters for it (that can transparently manipulate the arbitrary storage/rendering) would be a "best of both worlds" scenario.

Speaking as an end-user for a moment, the package seems fairly feature-complete to me, so if a future release a) breaks BC and b) doesn't give me compelling new features, I would be disinclined to follow that path.

[clue]

It seems to me that retaining getWeight/setWeight as an interface to the arbitrary attributes in a future version would allow you to retain BC.

Thanks for your input, I think this is a very valid point and we should consider keeping BC for the next version at least 👍

We will very likely still deprecate these methods and remove them in future versions, but keeping them for an intermediary release certainly makes sense 👍

While GraphML stores weights as an arbitrary attribute in representation, in practice the weight value is highly significant in that it differentiates a graph from a network. Tools like Gephi respect it as significant and change how they render the graph based on its presence.

I agree that edge weight (and family) is a significant attribute in certain cases, as that was also the main motivation to add them in the first place. However, we've seen several people ask for edges with multiple weights and other special attributes not possibly with the fixed properties. Besides, depending on your context, certain other attributes will be "significant", such as GraphViz layout attributes, which have already been removed in the previous release.

I understand that this may be frustrating as it require additional work, but this way we provide a clear upgrade path and plenty of time (ETA at least 6 months) to prepare for this change.