[GROOVY-2321] Sort fails on heterogenous collections

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.1-rc-2
• Fix Version/s: 1.1-rc-3
• Component/s: groovy-jdk
• Assignee: Paul King
• Reporter: Dirk Eßer
• Created: 19/Nov/07 08:37
• Updated: 22/Nov/07 05:19
• Resolved: 20/Nov/07 05:09

Description

Example Code:

class Foo implements Comparable {

    private int key

    public Foo(int k) {
        key = k
    }

    public int compareTo(Object rhs) {
        return key - rhs.key
    }

    public String toString() {
        return "foo: " + key
    }
}

class Bar extends Foo {
    
    public Bar(int x) {
        super(x)
    }
}

def listOfFoo = [
    new Foo(7),
    new Bar(6),
    new Foo(5),
    new Bar(4)
]

listOfFoo.sort()
println(listOfFoo)

Output of this script might be, for example (one cannot really tell, since the result is definitely VM/environment dependent):

groovy compareex.groovy
[foo: 6, foo: 5, foo: 7, foo: 4]

Reason: DefaultGroovyMethods.NumberAwareComparator: The default comparator used by the "sort()" implementation has a serious bug. Thanks to the test "o1.getClass() == o2.getClass()", the "compareTo" of class Foo won't be invoked whenever comparing a Foo with a Bar. This is – at best – counter-intuitive. You can work around this by providing a trivial comparator closure

{ x, y -> x.compareTo(y) }

.

This bug exists at least since version 1.0 (though the comparator class had a different name then)

Speaking about the NumberAwareComparator: is the "equals" method ever called? I hope it's not, since it looks suspiciously like an infinite recursion to me.