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https://issues.apache.org/jira/browse/TINKERPOP3-787?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14697748#comment-14697748
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Matt Frantz commented on TINKERPOP3-787:
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Another place to put this would be in {{GraphTraversalSource}}, with the intent
of affecting all container instantiation (in the data path) for the entire
traversal.
{code}
public <A extends Map> GraphTraversalSourceStub withMap(Supplier<A> s);
public <A extends Map> GraphTraversalSourceStub withMap(Class<A> c);
public <A extends List> GraphTraversalSourceStub withList(Supplier<A> s);
public <A extends List> GraphTraversalSourceStub withList(Class<A> c);
{code}
> User-defined containers
> -----------------------
>
> Key: TINKERPOP3-787
> URL: https://issues.apache.org/jira/browse/TINKERPOP3-787
> Project: TinkerPop 3
> Issue Type: Improvement
> Components: process
> Affects Versions: 3.0.0-incubating
> Reporter: Matt Frantz
> Assignee: Marko A. Rodriguez
>
> For any steps that create containers, we could add a modifier step (like
> {{by}}) that allows specifying a {{Supplier}} of that container.
> {noformat}
> <E2 extends List> GraphTraversal<S, E2> withList(Supplier<E2> s);
> <E2 extends Map> GraphTraversal<S, E2> withMap(Supplier<E2> s);
> {noformat}
> In addition to providing optimized container implementations, it could
> provide for application-specific derived container types, e.g. a Map subclass
> with accessor methods for particular keys.
> {noformat}
> class Student extends HashMap<String, Object> {
> public String name() { return (String)get("name"); }
> public int schoolAge() { return (Integer)get("schoolAge"); }
> }
> {noformat}
> This in turn allows stronger type safety for traversals, since you could
> declare the output of a Map-producing step to be your UDT.
> {noformat}
> g.V().as("name", "schoolAge")
> .select("name", "schoolAge")
> .<Student>withMap{->new Student()}
> .by(values("name")
> .by(out("school").values("age"))
> {noformat}
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