[GROOVY-4257] Collection.unique() method might remove not duplicate items

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.8-beta-1
• Component/s: groovy-jdk
• Environment: Windows XP, JDK 1.6.0_19, GROOVY 1.7.0
• Assignee: Paul King
• Reporter: Yixun Fang
• Created: 22/Jun/10 01:54
• Updated: 22/Jul/10 17:33
• Resolved: 23/Jun/10 15:39

Description

list=[[3035, 26972], [2795, 34412]]
list.unique()
println list

Result: [[3035, 26972]]

list=[[3035, 26972], [2795, 34412]]
list.unique

{it}

println list

Result: [[3035, 26972]]

Because the unique method use NumberAwareComparator<T> to compare elements in the collection, and NumberAwareComparator<T> will use object's hashCode to compare two object when the object doesn't have a compareTo method, then the two list [3035, 26972], [2795, 34412] are considered to be duplicate(because they have the same hashCode).

Will it be better to use equals method to decide whether two elements are duplicate?
As the document say:
"A convenience method for making a collection unique using a Closure to determine duplicate (equal) items. If the closure takes a single parameter, the argument passed will be each element, and the closure should return a value used for comparison (either using

{@link Comparable#compareTo(Object)}

or

{@link Object#equals(Object)}

). If the closure takes two parameters, two items from the collection will be passed as arguments, and the closure should return an int value (with 0 indicating the items are not unique)."