Groovy resolves ambiguous methods alphabetically by parameter class name

Question

Groovy will resolve ambiguous method calls by choosing the method with a parameter type that is alphabetically first. In the following example the method that takes a parameter of type "A" will be called if Groovy calls MyClass.printIt(null).

If you refactor this code to rename class A to class C you will find that the call with a null myVariable will then resolve to the method that takes a parameter of type "B", the bottom one.

    class MyTest {
      public static void main(String[] args) {
        B myVariable = new B()
        new MyClass().printIt(myVariable)
        myVariable = null
        new MyClass().printIt(myVariable)
      }
    }
    class A {}
    class B {}
    class MyClass {
      void printIt(A variable) {
        println "TOP method called"
      }
      void printIt(B variable) {
        println "BOTTOM method called"
      }
    }

the code as listed above produces the following output

BOTTOM method called

TOP method called it called the top method with a variable of type B

once class A is renamed to class C the output will change to

BOTTOM method called

BOTTOM method called

try as many permutations as you like, the method that takes the class with the lowest alphabetical name is called when the variable passed in is null, even if the variable is typed for the other class.

groovy --version Groovy Version: 2.0.5 JVM: 1.6.0_33 Vendor: Sun Microsystems Inc. OS: Windows 7

My question is why does Groovy do this, is this by design or is it a bug, is this behavior documented anywhere?

Dave

Answer 1

Can't reproduce this on groovy 2.1.6. Can't reproduce this on groovy 2.0.5 either. In both use cases output is:

BOTTOM method called
TOP method called

When A is renamed to C output is

BOTTOM method called
TOP method called

Gentoo Linux, JDK 1.7.0_25,