types - Groovy coercing List to Map doesn't throw ClassCastException or what is ArrayList1_groovyProxy? -

i writing code tried cast object map.

map = object map 

i alternatively use

map = (map) object 

and whole question irrelevant throws classcastexception if object of type list, using former encountered interesting thing. if object list, i.e. object = [], groovy type coercion behave different expected.

my expectation classcastexception, instead got resulting object. object seems odd. instance of list , instance of map , using .tostring() on resulted in output of list, not map ([a,b]). not possible set value on map a['c'] = 'c'. results in java.lang.illegalargumentexception: argument type mismatch.

map = ['a', 'b'] map  println(a) println(a instanceof list) println(a instanceof map) println(a.getclass()) 

results in following output:

[a, b] true true class arraylist1_groovyproxy 

i tried google find out arraylist1_groovyproxy is, couldn't find anything.

it still doesn't make sense me, coercion returns object not should , seems kind of broken, instead of throwing classcastexception.

can explain me reasoning behind behavior instead of throwing exception , explain use of arraylist1_groovyproxy? or bug in groovy?

the as operator calls astype method provided type argument method.

you can see default implementation astype in defaultgroovymethods.

since map interface, call proxygenerator.instance.instantiatedelegate(interfaces, obj), returns dynamic proxy implements map.

/**  * converts given object type. method used through  * "as" operator , overloadable other operator.  *  * @param obj  object convert  * @param type goal type  * @return resulting object  * @since 1.0  */ @suppresswarnings("unchecked") public static <t> t astype(object obj, class<t> type) {     if (string.class == type) {         return (t) invokerhelper.tostring(obj);     }      // fall cast     try {         return (t) defaulttypetransformation.casttotype(obj, type);     }     catch (groovycastexception e) {         metaclass mc = invokerhelper.getmetaclass(obj);         if (mc instanceof expandometaclass) {             expandometaclass emc = (expandometaclass) mc;             object mixedin = emc.casttomixedtype(obj, type);             if (mixedin != null)                 return (t) mixedin;         }         if (type.isinterface()) {             try {                 list<class> interfaces = new arraylist<class>();                 interfaces.add(type);                 return (t) proxygenerator.instance.instantiatedelegate(interfaces, obj);             } catch (groovyruntimeexception cause) {                 // ignore             }         }         throw e;     } 

as why groovy goes such great lengths coerce types--it's nature of groovy: making java coding easier. can construct object passing map constructor, or coerce map instance particular type; why not let every object coerced map via as operator?