[
https://issues.apache.org/jira/browse/JEXL-316?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16943401#comment-16943401
]
Dmitri Blinov commented on JEXL-316:
------------------------------------
I have checked how in other languages the position of the null-coalescing
operator is defined, and results are very mixed. The languages like C#,
Javascript (being proposed) place null coalescing operand closer to ternary,
like it is currently implemented in JEXL. Some languages like PHP and
freemarker are closer to what is being proposed. There are some like Swift that
are in between - above the arithmetic, but below comparisons. Some languages do
not have null coalescing operator at all, but use *elvis* operator for this
purpose, which they BTW, see as shortened form of ternary operator. For me, for
example, this is also comes as no surprise - I get used to elvis being a
ternary sibling, not a null coaliscing one. In some sence, IMO, the
introduction of null coalescing operator in JEXL is more justified when it
differs from what we have already had.
So, the community has no single approach to the problem, and no industry-wide
convention. Lets leave it as it is for now.
> Operator ?? has very low priority
> ---------------------------------
>
> Key: JEXL-316
> URL: https://issues.apache.org/jira/browse/JEXL-316
> Project: Commons JEXL
> Issue Type: Bug
> Affects Versions: 3.1
> Reporter: Dmitri Blinov
> Assignee: Henri Biestro
> Priority: Major
> Fix For: 3.2
>
>
> In current version of JEXL the script
> {code:java}
> 10??0 + 200 {code}
> evaluates to 10, which is counterintuitive. It requires to always use
> parantheses after {{\\??}}. The operator {{??}} should have higer priority.
> It is the same problem as with current version of freemarker, but they
> promise to fix it in the next major release.
> The suggestion is to set priority of operator {{??}} to be between
> {{UnaryExpression()}} and {{ValueExpression()}}
> {code}
> void ConditionalExpression() #void : {}
> {
> ConditionalOrExpression()
> (
> <QMARK> Expression() <COLON> Expression() #TernaryNode(3)
> |
> <ELVIS> Expression() #TernaryNode(2)
> )?
> }
> ...
> void UnaryExpression() #void : {}
> {
> <minus> UnaryExpression() #UnaryMinusNode(1)
> |
> <plus> UnaryExpression() #UnaryPlusNode(1)
> |
> <tilda> UnaryExpression() #BitwiseComplNode(1)
> |
> (<not>|<NOT>) UnaryExpression() #NotNode(1)
> |
> <EMPTY> UnaryExpression() #EmptyFunction(1)
> |
> <SIZE> UnaryExpression() #SizeFunction(1)
> |
> NullpExpression()
> }
> void NullpExpression() #void : {}
> {
> ValueExpression()
> (
> <NULLP> ValueExpression() #NullpNode(2)
> )*
> }
> {code}
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
