Scott Murphy Heiberg created GROOVY-12613:
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Summary: Compound assignment in a trait method evaluates its
target twice when the target is not a trait field
Key: GROOVY-12613
URL: https://issues.apache.org/jira/browse/GROOVY-12613
Project: Groovy
Issue Type: Bug
Affects Versions: 5.0.8, 4.0.33, 6.0.0
Reporter: Scott Murphy Heiberg
{code:groovy}
trait T {
def m() { def l = [0, 0]; int i = 0; l[i++] += 1; [i, l] }
}
class C implements T {}
assert new C().m() == [1, [1, 0]]
{code}
Actual: {{new C().m()}} returns {{[2, [1, 0]]}}. The index expression runs
twice. The same method in a class returns {{[1, [1, 0]]}}. The receiver or
subscript of any compound assignment in a trait method is evaluated twice, for
example a map subscript key() is called twice. This happens with and without
@CompileStatic / @TypeChecked.
Expected: {{[1, [1, 0]]}}. A compound assignment evaluates its target once, as
it does in a class.
Cause: the trait transformation (NAryOperationRewriter) rewrites every compound
assignment in trait code into a plain assignment (a = a op b). The rewrite is
only needed when the target is a trait field, which becomes a field-helper
getter/setter call.
Seen in 4.0.33, 5.0.8 and 6.0.0.
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