[GROOVY-7464] Iterable.intersect() is not commutative (and allows duplicates)

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Won't Fix
• Affects Version/s: 2.4.3
• Component/s: groovy-jdk
• Assignee: Paul King
• Reporter: Peter Ledbrook
• Created: 11/Jun/15 12:39
• Updated: 16/Apr/18 05:32
• Resolved: 16/Apr/18 05:32

Description

The intersect() method on Iterable has different results depending on the order of the receiver object and the argument. For example,

def a = [1, 1, 2, 4]
def b = [1, 2, 2, 3]

println a.intersect(b)
println b.intersect(a)

prints out two different results ([1, 1, 2] and [1, 2, 2]).

Assuming that the operation should be commutative, i.e. the results should be the same for both, the question then becomes whether duplicates should even be returned at all.

I think the method should always return a set as intersection is a set operation. In other words, Iterable.intersect() becomes a convenience wrapper that converts the receiver object and the argument to sets.

This issue started as a discussion on the dev mailing list.