[GROOVY-10108] Tuple constructor fails for an @Immutable class having a single Map property

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.5.0, 2.5.14, 3.0.8
• Fix Version/s: 4.0.7
• Environment: N/A
• Assignee: Eric Milles
• Reporter: Douglas Paul
• Created: 25/May/21 14:55
• Updated: 10/Feb/23 21:40
• Resolved: 21/Nov/22 23:11

Description

For an @Immutable class having a single Map property, trying to use the generated tuple constructor generally results in an exception being thrown from ImmutableASTTransformation.checkPropNames(). This did not happen in Groovy 2.4.

For example, given a class like this:

@Immutable
class LookupTable {
    Map<Long, String> data
}

And this usage of that class:

Map<Long, String> data = [(1L): 'foo', (2L): 'bar']
new LookupTable(data)

The constructor invocation throws:

java.lang.ClassCastException: java.lang.Long cannot be cast to java.lang.String
	at org.codehaus.groovy.transform.ImmutableASTTransformation.checkPropNames(ImmutableASTTransformation.java:423)

The documentation for @Immutable does mention there are limitations when there is a single property of type Map, but the wording there doesn't sound like it's talking about the tuple constructor:

Groovy's normal map-style naming conventions will not be available if the first property has type LinkedHashMap or if there is a single Map, AbstractMap or HashMap property.

In fact that wording makes it sound as if it's the map-based constructor that won't be available, when in fact using the map-based constructor does work in this case (and thus seems to be a viable workaround).

See https://github.com/douglyuckling/groovy-2.5-immutable-with-map-bug for a minimal reproduction of the problem.

Issue Links

• relates to: GROOVY-8416 Map-based constructor generated by @Immutable works only with HashMap