What is the simplest way to cast a Map<Object, List<SObject>>?

Question

I'm trying to find the most simple way to cast a map<Object, List<Sobject>> in any other type like, String, Integer and etc..

Anyone knows how to do this?

This is my code

Map<Object, SolicitationItem__c[]> mapHierarchyRequestToItem = (Map<Id,SolicitationItem__c[]>) Collection.of(newRecordsMap.values()).group().byField(SolicitationItem__c.HierarchySolicitation__c).get();

ERROR:

Incompatible types since an instance of Map<Object,List> is never an instance of Map<Id,List<SolicitationItem__c>> (11:72)

Answer 1

Simplifying things greatly, sets (and the keysets of maps) do not contain enough type information for you to cast between different types. I had a question that went over this in greater detail (Is there a specific reason why we can't upcast sets?)

Lists can be cast, and Maps can be cast as long as the key type isn't changing. Sets can never be cast (at time of writing).

If your mapHierarchyRequestToItem map contains Ids as the key, you'll need to extract them one by one inside of a loop.

e.g.

Set<Id> extractedIds = new Set<Id>();
for(Object data :myMap.keySet()){
    // You can't cast the set, so you need to cast the individual items in the set
    extractedIds.add((Id)data);
}