Hi all,
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
