How to convert from ICollection to IEnumerable?

Question

In the below code the return statement is throwing exception.

private IEnumerable<DirectoryEntry> GetDomains()
{
    ICollection<string> domains = new List<string>();

    // Querying the current Forest for the domains within.
    foreach (Domain d in Forest.GetCurrentForest().Domains)
    {
        domains.Add(d.Name);
    }

    return domains;  //doesn't work
}

What could be the possible resolution to this issue?

Solution 1

Redefine your method as

private IEnumerable<string> GetDomains()
{
    ...
}

since you're wanting a list of string and not Domains or DirectoryEntry. (assumed since you're adding "d.Name")

Also, it would be much easier to just use LINQ:

IEnumerable<string> domains = Forest.GetCurrentForest().Domains.Select(x => x.Name);

This will return an IEnumerable<string>, and it won't waste extra memory creating a separate list.

Solution 2

Set the type of domains to IList<string> or do as Nathan suggests:

private IEnumerable<string> GetDomains()
{
  return Forest.GetCurrentForest().Domains.Select(x => x.Name);
}