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From "Matt Benson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (COLLECTIONS-461) splitmap.TransformedMap is not really a Map
Date Mon, 13 May 2013 23:19:15 GMT

    [ https://issues.apache.org/jira/browse/COLLECTIONS-461?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13656508#comment-13656508
] 

Matt Benson commented on COLLECTIONS-461:
-----------------------------------------

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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