Can I cast a map from <String, SObject> to <String, MyObject>?

Question

It seems like no. I have a utility method

   public static Map<String, SObject> getMapOfStringToSObject(List<SObject> lstSObjs, String strKeyFieldName)
   {
       Map<String, SObject> mapStringToSObject = new Map<String, SObject>();
       for (SObject so : lstSObjs)
           mapStringToSObject.put((String)so.get(strKeyFieldName), so);

       return mapStringToSObject;
   }

But when I try to use it (with casting) I get System.TypeException: Invalid conversion from runtime type Map<String, SObject> to Map<String, MyObject> ()

Client code is

Map<String, MyObject> res = (Map<String, MyObject>)UtilsClass.getMapOfStringToSObject(someList, 'someStringField');

Sure I could not cast and loop over the results. But the whole point of this is to abstract away the looping and not have to write it over and over. I have similar methods (where I can cast successfully) that return a variety of types including among others

Map<String, List<SObject>>
Map<Id, List<SObject>>

Answer 1

Provided that MyObject is an SObject (which it should be, given your code so far), the best I've been able to come up with is something like

Map<String, MyObject> res = new Map<String, MyObject>(UtilsClass.getMapOfStringToSObject(someList, 'someStringField').values());

Which makes use of the map constructor which takes a list.

Unfortunately, that forces you to use the record Id as the map key. In limited situations, you could use the field aliasing trick (in a query that uses GROUP BY) to make some other field be the "Id", but I have a feeling that's not going to work for your utility class.

I don't think it's practical to avoid a loop here.

Answer 2

I found a way to do this that's only slightly clunky. If I tell my method the return type I want, I can instantiated it with newInstance()

public static Map<String, SObject> getMapOfStringToSObject(List<SObject> lstSObjs, String strKeyFieldName, Type mapType)
{
    Map<String, SObject> mapStringToSObject = (Map<String, SObject>) mapType.newInstance();
    for (SObject so : lstSObjs)
        mapStringToSObject.put((String)so.get(strKeyFieldName), so);

    return mapStringToSObject;
}

And client code:

Map<String, Account> res = (Map<String, Account>)UtilsCollection.getMapOfStringToSObject(accounts, 'Name', Map<String, Account>.class);

Answer 3

You can use:

Map<String, SObject> mapStringToSObject = new Map<String, SObject>();

   Map<String, MyObject> result = (Map<String, MyObject>) JSON.deserializeStrict(JSON.serialize(mapStringToSObject),Map<String, MyObject>.class);