Step - map

map(traversal) replaces each traverser's value by the first result of a child traversal run on it (TinkerPop TraversalMapStep). A traverser for which the child yields nothing is dropped.

g.V("1").out().map(__.values("name")).to_list()                       // ["josh", "lop", "vadas"]
g.V().map(__.out("created").values("name")).to_list()                 // ["lop", "ripple", "lop"]
g.V().as("a").out("created").map(__.select("a").values("name")).to_list()
// ["marko", "josh", "josh", "peter"]

• The child sees the incoming traverser with its path, sack and labels, so select("a") inside the child reads an as("a") before map().
• The result is one new path position: the child's own steps do not show up in a later path().
• null is a result like any other: g.V().map(__.constant(())) yields six nulls.
• Bulk is kept: a merged traverser maps once and keeps its bulk.

For every result of the child instead of the first, use flatMap(). withPath() is accepted on g for Gremlin compatibility and changes nothing: Graphersal records the path positions a query reads on its own. Like withSack(), it is a source step: inside a child traversal (__.withPath()) it fails before execution with SourceStepInChild, as __.withSack(1) does.

Rust: GraphTraversalSource::map(traversal), __::map(traversal).