Sorry all - sent without a subject, so resending to correct that.
I sent this to groovy-users but didn't get much response. I am trying to
> understand some behaviour that is causing subtle and odd bugs in our code,
> which might be a bug or might be something I don't understand.
>
> The behaviour is that under very specific circumstances, Groovy is
> coercing a List of Maps to a single Map. A condensed example is
>
> class Foo {
> def foo(Map obj) {
> println(obj)
> }
> }
> z = [
> [ a: 1, b:2]
> ]
> f = new Foo()
> f.foo(z)
>
> In here, even though the foo() method requires a Map, the call does not
> throw a type mismatch exception. Instead, the foo() method receives the Map
> object that is the first entry of the list as its argument. Consequently,
> it prints:
>
> [a:1, b:2]
>
> If instead, it is passed a list containing two Maps, eg: z = [ [ a: 1,
> b:2], [c:1, d:2] ], then it does throw a type conversion error. Also
> notable is that it will always throw the type conversion error if you
> attempt to coerce it outside the context of a function call, for example,
> using z.asType(Map).
>
> So it seems that under very specific circumstances that is both code
> context and data dependent, Groovy will perform a different type of type
> conversion to what it would do otherwise, but this is data dependent which
> is a bit unsatisfying.
>
> Can anyone explain why it does this and what the rationale is? Or is it
> actually a bug?
>
Cheers,
Simon
