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https://issues.apache.org/jira/browse/VELOCITY-917?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16853844#comment-16853844
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Claude Brisson commented on VELOCITY-917:
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And from my last tests, it looks like it will be too difficult to patch the
parser token manager class file, because even with a single character change in
the grammar, the differences are too great in the token manager file. Well. It
was an experiment.
The best we can achieve is to provide an alternate parser, as a directly
available solution (`parser.class = StandardParser | TailoredParser`) or as
development trail for Velocity hackers. _Tailored_ was initially chosen because
it had the same number of letters as _Standard_, easing a later patching
process, but I guess _Custom_ will do as well.
> VTL Grammar Characters Configuration
> ------------------------------------
>
> Key: VELOCITY-917
> URL: https://issues.apache.org/jira/browse/VELOCITY-917
> Project: Velocity
> Issue Type: New Feature
> Components: Engine
> Affects Versions: 2.2
> Reporter: Claude Brisson
> Assignee: Claude Brisson
> Priority: Major
>
> Experimental feature.
> The goal is to introduce new configuration parameters to be able to change
> the VTL grammar. For instance:
> parser.character.dollar = '~'
> parser.character.hash = '@'
> parser.character.arobase = '%'
> parser.character.star = '?'
> Requirements:
> + fully B.C.
> + done at runtime, without the need to recompile the parser
> + null impact on performance
> Implementation:
> 1. Parametrize code that needs explicit references to those characters
> 2. Define a ParserTokenManager interface and have the parser use this
> interface rather than a concrete class
> 3. Use a custom class loader to *patch* the concrete token manager .class
> file, instantiate this custom token manager and initialize parsers with it
> The binary patch is prepared at compilation time (there will be one patch per
> JRE vendor and class file version).
> Due to the limited capability of this technique, the chosen characters are
> restricted to UTF-8 single bytes characters. Patches _could_ be prepared for
> two-bytes or more characters, but there would be the need to have as many
> parser objects as variants in one/two/... characters combinations.
> Also, some characters and combinations are obviously invalid.
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