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https://issues.apache.org/jira/browse/JEXL-307?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16941873#comment-16941873
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Henri Biestro commented on JEXL-307:
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Of course, the behaviour wrt local variables / parameters is what you describe
(besides your penultimate example which is not allowed for the same reason the
2nd is not, if or no-if or for or while).
I'll restate we only have 2 scopes today; global variables (JexlContext) and
local variables whose scope is the whole function/lambda after their point of
declaration. Locals so far have the weak(er) Javascript-like 'var' semantic.
The idea is to allow turning gracefully to a 'let'-like one (aka lexical scope)
without adding yet another keyword. Pretty much the same rules Java or C apply
wrt to local variable definition in this mode. The solution will *not* change
any existing behaviour, current code under current configuration will run the
same way.
Setting the lexical feature - at JexlEngine construction time - and/or the
lexical option - plus at script evaluation time - will trigger the new semantic
on variable scopes. Using the option, it will be even possible to turn it
on/off in the script itself through a pragma.
This allows existing users dealing with huge scripts to easily control the pace
of deploying this lexical semantic.
> Variable redeclaration option
> -----------------------------
>
> Key: JEXL-307
> URL: https://issues.apache.org/jira/browse/JEXL-307
> Project: Commons JEXL
> Issue Type: New Feature
> Affects Versions: 3.1
> Reporter: Dmitri Blinov
> Assignee: Henri Biestro
> Priority: Minor
> Fix For: 3.2
>
>
> As of now, JEXL allows a script writer to redeclare a local variable during
> script evaluation.
> {code:java}
> var a = 1; var a = 2;{code}
> This may lead to potential errors with misspelled names and clashed
> variables. Checking for already defined variable is a common feature of many
> languages. This feature can be implemented in JEXL as an additional option of
> JexlFeatures class, enabled by default, thus allowing compatibility with
> existing code.
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