Collection read only : Unable to add to set

Question

I have to populate a set of Ids with Ids derived from a List<List<sObject>> say searchlist. Below code as I am trying gives me System.Final Exception as Collection is read only and prevents me to copy over Ids from Set<Id> tempids to Set<Id> accids.

Apex Code

  accids = new Map<Id,SObject>(searchList[0]).keySet();
        for(List<sObject> s: searchList)
        tempids = (new Map<Id,SObject>(s)).keySet();
        accIds.addall(tempids);

Can someone please let me know what's wrong going on here?

Answer 1

Caspar's comment explains the problem. You are trying to use the keySet() of a Map in a way that is not intended: those are intended to simplify code that reads the values and are not intended for use as a general purpose set.

So instead create your own mutable (writeable) set:

Set<Id> accIds = new Set<Id>();
for(List<sObject> sob: searchList) {
    Set<Id> tempIds = (new Map<Id,SObject>(sob)).keySet();
    accIds.addAll(tempIds);
}

Personally I would write the logic like this:

Set<Id> accIds = new Set<Id>();
for(List<sObject> sobs: searchList) {
    for(sObject sob: sobs) {
        accIds.add(sob.Id);
    }
}

Answer 2

Thanks everyone! I was able to fix the issue with Caspar Hammer's suggestion. Thanks!

 accids = new Map<Id,SObject>(searchList[0]).keySet().clone();

for(List<sObject> sob: searchList) {
    Set<Id> tempIds = (new Map<Id,SObject>(sob)).keySet();
    accIds.addAll(tempIds);
}