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https://issues.apache.org/jira/browse/TINKERPOP3-800?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15007219#comment-15007219
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Marko A. Rodriguez commented on TINKERPOP3-800:
-----------------------------------------------

[~rjbriody] -- can you provide your thoughts on the importance of this so when 
we go over placing tickets for versions, we know your use case and can argue 
its priority better?

> [Proposal] Domain/Range checking during traversal construction.
> ---------------------------------------------------------------
>
>                 Key: TINKERPOP3-800
>                 URL: https://issues.apache.org/jira/browse/TINKERPOP3-800
>             Project: TinkerPop 3
>          Issue Type: Improvement
>          Components: process
>    Affects Versions: 3.0.2-incubating
>            Reporter: Marko A. Rodriguez
>            Assignee: Marko A. Rodriguez
>
> I think we should add two new methods to {{Step}}.
> {code}
> Step.getDomain() -> Class
> Step.getRange() -> Class
> {code}
> Now, when someone does:
> {code}
> g.V().out()
> {code}
> {{GraphStep}} will report that its range is {{Vertex.class}}. {{VertexStep}} 
> will report its domain to be {{Vertex.class}}. Good. No typing issues. 
> However, when you do this:
> {code}
> g.E().out()
> {code}
> {{GraphStep}} will report that its range is {{Edge.class}}. {{VertexStep}} 
> will report its domain to be {{Vertex.class}} --- {{IllegalArgumentException: 
> "The provided traversal has an illegal function composition."}}.
> Why is this good -- much better than getting random {{ClassCastExceptions}} 
> at execution time.



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