Step - concat

concat(string...) appends strings to the string a traverser holds; concat(traversal...) appends the first result of each child traversal, run on the incoming traverser (its path included). The arguments are all strings or all traversals. Without an argument the string passes unchanged.

graphersal> g.V().hasLabel("software").as("s").values("name").concat(" uses ").concat(__.select("s").values("lang")).to_list()
"lop uses java"
"ripple uses java"

graphersal> g.V("1").outE("created").as("e").V("1").values("name").concat(__.select("e").label(), __.select("e").inV().values("name")).to_list()
"markocreatedlop"

graphersal> g.inject("a").concat(__.inject("c")).to_list()
"aa"

The last example shows the first-result rule: __.inject("c") yields the incoming "a" first.

null

A null is skipped wherever it occurs, as the incoming value, as a constant (() in Rhai) or as a child result. The result is null only when everything was null:

graphersal> g.inject((), "a").concat((), "b").to_list()
"b"
"ab"

graphersal> g.inject(()).concat().to_list()
()

Errors

• An incoming value that is neither a string nor null is a cast error. Convert it first, for example values("age").as_string().concat(" years old").
• A constant argument that is neither a string nor null (concat(1)) is rejected before the traversal runs.
• A child traversal that yields nothing, or a value that is not a string, is a ValueError::StringFunctionInput. Make the child always produce a string, for example with coalesce(..., constant("")) or as_string().

Rust API: concat(vec!["a", "b"]) (a null argument is ElementProperty::Null) and concat_traversal(vec![__::select("a").values("lang")]).