Alias S2Builder.Label

Every edge can have a set of non-negative integer labels attached to it. When used with an appropriate layer type, you can then retrieve the labels associated with each output edge. This can be useful when merging or combining data from several sources. (Note that in many cases it is easier to use separate output layers rather than labels.)

class S2Builder
{
  // ...
  alias Label = int;
  // ...
}

Labels are 32-bit non-negative integers. To support other label types, you can use ValueLexicon to store the set of unique labels seen so far:

ValueLexicon my_label_lexicon; builder.set_label(my_label_lexicon.Add(label));

The current set of labels is represented as a stack. This makes it easy to add and remove labels hierarchically (e.g., polygon 5, loop 2). Use set_label() and clear_labels() if you need at most one label per edge.