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Date: Fri, 6 Feb 2009 05:20:00 -0800 (PST)
From: "Rob Walker (JIRA)" <jira@apache.org>
To: issues@commons.apache.org
Subject: [jira] Commented: (CONFIGURATION-363) Consider enhancing to allow
 nested variable interpolation
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    [ https://issues.apache.org/jira/browse/CONFIGURATION-363?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12671120#action_12671120 ] 

Rob Walker commented on CONFIGURATION-363:
------------------------------------------

It looks like this would be an enhancement to the StrSubstitution class in Commons Lang.

Will raise a JIRA their and also see if I can figure and submit a patch

> Consider enhancing to allow nested variable interpolation
> ---------------------------------------------------------
>
>                 Key: CONFIGURATION-363
>                 URL: https://issues.apache.org/jira/browse/CONFIGURATION-363
>             Project: Commons Configuration
>          Issue Type: Improvement
>          Components: Interpolation
>            Reporter: Rob Walker
>            Priority: Minor
>
> It would be really handy of Commons Configuration could support nested variable interpolation:
> org.osgi.framework.system.packages=org.osgi.framework; version=1.4.0, \
>  org.osgi.service.packageadmin; version=1.2.0, \
>  org.osgi.service.startlevel; version=1.1.0, \
>  org.osgi.service.url; version=1.0.0, \
>  org.osgi.util.tracker; version=1.3.3 \
>  ${jre-${java.specification.version}}
> The process being to expand innermost variable references first and work outwards - this allows for very advance config, such as the above, which can dynamically detect the Java version and expand a JRE version specific property into the property being defined.
> Care is needed to avoid recursion, which can been handled through use of a "Cycle Map" that detects of an inner variable has already been referenced. 
> An example of this can be found in the substVars method of the Apache Felix org.apache.felix.framework.util.Util class.

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