I am not sure I have the full history of when support started (at least 15+ years ago) but dynamic Groovy unwraps a list as arguments:
def avg(int a, int b, int c) { (a + b + c)/3 } assert avg(1, 2, 3) == 2 // normal invocation def nums = [10, 20, 30] assert avg(nums) == 20 // args are a list It will only do this if the argument is a single List and no method matching a single List argument was found. Relevant implementation: https://github.com/apache/groovy/blob/master/src/main/java/groovy/lang/MetaClassImpl.java#L1242 https://github.com/apache/groovy/blob/master/src/main/java/groovy/lang/MetaClassImpl.java#L1246-L1253 You can turn this feature off with @TypeChecked/@CompileStatic. Cheers, Paul. <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> Virus-free.www.avast.com <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> On Sat, Mar 9, 2024 at 7:58 AM Simon Sadedin <ssade...@gmail.com> wrote: > > Hi, > > I am trying to understand some behaviour that is causing subtle and odd bugs > in our code. > > The behaviour is essentially 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. > > Can anyone explain why it does this and what the rationale is? > > Cheers, > > Simon