Iterator adaptor .positions(predicate)

[bluss]

Like an iterated version of position or a filtered version of enumerate.

The existing combination is a bit heavy on the punctuation:

self.1.iter()
      .enumerate()
      .filter(|&(_, node)| node.weight.is_none())
      .map(|(i, _)| NodeIndex::<Ix>::new(i))

Propose instead:

self.1.iter()
      .positions(|node| node.weight.is_none())
      .map(NodeIndex::<Ix>::new)

[bluss]

An alternative, a literal filtered version of enumerate. Indices are including the removed elements, of course.

self.1.iter()
      .enumerate_filter(|node| node.weight.is_none())
      .map(|(i, _node)| NodeIndex::<Ix>::new(i))

[tmccombs]

I prefer the positions interface, because it is easier to use in situations like

let positions = self.1.iter().positions().collect();