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https://issues.apache.org/jira/browse/GROOVY-12619?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18135952#comment-18135952
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ASF GitHub Bot commented on GROOVY-12619:
-----------------------------------------
paulk-asert opened a new pull request, #3156:
URL: https://github.com/apache/groovy/pull/3156
(no comment)
> Compound assignment and increment on a property evaluate the receiver
> expression twice
> --------------------------------------------------------------------------------------
>
> Key: GROOVY-12619
> URL: https://issues.apache.org/jira/browse/GROOVY-12619
> Project: Groovy
> Issue Type: Bug
> Affects Versions: 4.0.33, 5.0.8, 6.0.0
> Reporter: Scott Murphy Heiberg
> Priority: Major
>
> {code:groovy}
> class Box { int v = 1 }
> class C {
> int calls = 0
> Box box = new Box()
> Box obj() { calls++; box }
> def m() { obj().v += 2; [calls, box.v] }
> def n() { obj().v++; [calls, box.v] }
> }
> assert new C().m() == [1, 3]
> assert new C().n() == [1, 2]
> {code}
> Actual: m() returns [2, 3] and n() returns [2, 2]. The receiver obj() is
> called once for the read of the property and again for the write. The same
> happens in dynamic Groovy, under @TypeChecked and under @CompileStatic. It
> also happens for prefix and postfix increment and decrement, attribute access
> ({{obj().@f += 2}}), safe navigation ({{obj()?.v += 2}}), chains with a
> side-effecting getter, static properties reached through an instance, and
> extension properties such as File text. Under @CompileStatic, {{obj().d++}}
> on a BigDecimal property calls obj() three times.
> Expected: the receiver is evaluated once, before the right-hand side, and
> reused for the read and the write. Subscripts already behave this way
> (GROOVY-12098).
> Cause: the code generator evaluated the property expression once as an rvalue
> and once as the assignment target. The static compiler's rewrites to x.p =
> x.p.op\(y) and to the extension setter reused the receiver expression on both
> sides. The elvis assignment form is GROOVY-12515.
> Seen in 4.0.33, 5.0.8 and 6.0.0.
> PR: https://github.com/apache/groovy/pull/3145
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