[jira] [Commented] (VELOCITY-917) VTL Grammar Characters Configuration

["Sergiu Dumitriu (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/VELOCITY-917?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16853379#comment-16853379 ] 

Sergiu Dumitriu commented on VELOCITY-917:
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I would prefer more semantic names for the parameters, such as {{parser.character.variable}}, {{.directive}}, {{.silent}}, {{.formalNotationStart}} and {{.formalNotationEnd}}.

> 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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