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https://issues.apache.org/jira/browse/COLLECTIONS-461?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13656508#comment-13656508
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Matt Benson commented on COLLECTIONS-461:
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Riight... I hadn't looked at this stuff in years. {{TransformedMap}} narrows
the RT from {{Object}} to return {{V}} from {{#put(J, U)}} and in that sense
will never behave like a regular {{Map}}--my point being that we don't know how
to "untransform" the value back to the {{U}} type. Returning the value
actually contained in the target map is the best we can do. The proposed
{{#putTransformed()}} method would still suffer the same problem: no way to
get back to a {{U}} type from the {{V}} contained in the decorated {{Map}}. Is
the issue that {{TransformedMap}} is still named \*Map? It was my intent that
placing it in the {{splitmap}} subpackage would, along with
[http://svn.apache.org/viewvc/commons/proper/collections/trunk/src/main/java/org/apache/commons/collections4/splitmap/package-info.java?view=markup],
make the intent clear: namely, that a "split map" is like a "map" but is
really a combination of {{Get}}/{{Put}} with no guarantees as to the type
assignability between the two. This was the only approach I found at the time
to allow the preservation of the functionality of {{TransformedMap}} while also
permitting it to be fully genericized.
> splitmap.TransformedMap is not really a Map
> -------------------------------------------
>
> Key: COLLECTIONS-461
> URL: https://issues.apache.org/jira/browse/COLLECTIONS-461
> Project: Commons Collections
> Issue Type: Bug
> Reporter: Sebb
> Fix For: 4.x
>
>
> splitmap.TransformedMap is part of the Get/Put hierarchy, but it does not
> behave like a proper Java Map.
> In particular, java.util.Map.put(K, V) returns V.
> However the collections Put interface returns Object.
> As far as I can tell, this was done in order to be able to include
> TransformedMap in the hiearchy. But the side effect is to break the generics
> for all the non-transformer maps in the hierarchy.
> Maybe there should be a separate PutTransformed interface which has the
> appropriate generic types, i.e.
> public T put(K key, V value)
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