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https://issues.apache.org/jira/browse/TINKERPOP-3015?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17798300#comment-17798300
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Christopher Smith commented on TINKERPOP-3015:
----------------------------------------------
There exists a compilation error with that exact code in 3.5, and I suspect it
also exists in 3.6 and 3.7. Specifically, even if your code words by
coincidence, I believe inspecting the generated bytecode (e.g., with {{javap
-v}}) will show that the wrong overload is being selected.
{code}Collection<String> asString = List.of("a", "b");
@SuppressWarnings({ "unchecked", "rawtypes" })
Collection<Object> asObject = (Collection) asString;
gts.V().hasId(P.within(asString)).iterate();
gts.V().hasId(P.within(asObject)).iterate();
{code}
correctly produces the following bytecode snippet, where you can see that the
invocation of {{hasId(P<String>)}} is resolved to {{hasId(Object, Object...)}}
{code}
#60 = InterfaceMethodref #61.#63 //
org/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversal.hasId:(Ljava/lang/Object;[Ljava/lang/Object;)Lorg/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversal;
#61 = Class #62 //
org/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversal
#62 = Utf8
org/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversal
#63 = NameAndType #64:#65 //
hasId:(Ljava/lang/Object;[Ljava/lang/Object;)Lorg/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversal;
#64 = Utf8 hasId
#65 = Utf8
(Ljava/lang/Object;[Ljava/lang/Object;)Lorg/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversal;
#66 = InterfaceMethodref #61.#67 //
org/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversal.iterate:()Lorg/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversal;
#67 = NameAndType #68:#69 //
iterate:()Lorg/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversal;
#68 = Utf8 iterate
#69 = Utf8
()Lorg/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversal;
#70 = InterfaceMethodref #61.#71 //
org/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversal.hasId:(Lorg/apache/tinkerpop/gremlin/process/traversal/P;)Lorg/apache/tinkerpop/gremlin/process/traversal/dsl/graph/GraphTraversal;
{code}
The fact that this produces the desired results in the current implementation
is an implementation detail and not guaranteed by the API semantics.
> Use wildcard instead of Object for hasId predicates
> ---------------------------------------------------
>
> Key: TINKERPOP-3015
> URL: https://issues.apache.org/jira/browse/TINKERPOP-3015
> Project: TinkerPop
> Issue Type: Improvement
> Affects Versions: 3.5.7, 3.6.5
> Reporter: Christopher Smith
> Priority: Minor
>
> From both {{GraphTraversal}} and {{__}}, the {{hasId(P)}} steps specify a
> {{P<Object>}}. Common predicates, such as {{within}}, propagate the generic
> type from their own arguments, so that this produces a compile-time error:
> {code}
> Collection<String> ids = ...
> g.V().hasId(P.within(ids))
> {code}
> I believe that without loss of safety, the signature in both locations could
> be changed to {{P<?>}}, making the typical case of "here's a collection of
> IDs of known type" work smoothly.
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