c# recursion - "Collection was modified; enumeration operation may not execute"

Question

I am trying to use recursion to go up a hierarchy, and i get this error:

Collection was modified; enumeration operation may not execute.

My assumption here is that when it enters the function each time, it is using the same parentRolesCopy and not a different one, so when it enters in the second time it changes parentRolesCopy to be different in the original function call.

How can I get around this?

private IEnumerable<string> GetAllParentRoles(string role)
    {
        // GET EACH PARENT ROLE
        var parentroles = //code that gets any parents of the role passed in


        //RECURSIVELY CALL THIS FUNCTION TO KEEP GETTING PARENTS OF PARENT ROLES UNTIL NONE LEFT
        var parentRolesCopy = parentroles;
        foreach (var parentrole in parentRolesCopy)
        {
            parentroles.AddRange(GetAllParentRoles(parentrole));
        }

        return parentroles;
    }

You're only copying the reference. They both point to the same actual collection. — Brian Rasmussen, Aug 29 '12 at 17:09

score 4 · Accepted Answer · answered Aug 29 '12 at 17:07

4

You can make the copy actually be a copy instead of just pointing to the same reference. One way would be:

var parentRolesCopy = parentroles.ToArray();

answered Aug 29 '12 at 17:07

itsme86

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Ah, thanks! I didn't realize what I was doing was just making a reference to the original. – Kyle Aug 29 '12 at 17:11

score 2 · Answer 2 · answered Aug 29 '12 at 17:07

2

You can use List or some other collection

var parentRolesCopy = new List<string>(parentroles);

answered Aug 29 '12 at 17:07

L.B

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c# recursion - "Collection was modified; enumeration operation may not execute"

2 Answers2