Most efficient way to parse a flagged enum to a list

Question

I have a flagged enum and need to retrieve the names of all values set on it.

I am currently taking advantage of the enum's ToString() method which returns the elements comma-separated.

    public void SetRoles(Enums.Roles role)
    {
        IList<Entities.Role> roleList = role.ToString("G").Split(',')
            .Select(r => new Entities.Role(r.Trim()))
            .ToList();
    ...
    }

I'm sure there must be a better way than this.

Answer 1

Why do you need a list? Everything is already stored in the flags:

[Flags]
enum Roles
{
    Read = 0x1,
    Write = 0x2,
    Delete = 0x4,
}

Then assign roles:

var roles = Roles.Read | Roles.Write;

And whenever you need to check if a given role has been you don't need to look in a list, but simply look in the roles enumeration:

if ((roles & Roles.Read) == Roles.Read)
{
    // The user has read permission
}
if ((roles & Roles.Write) == Roles.Write)
{
    // The user has write permission
}

Answer 2

Good question!

I can't think of anything better than:

public void SetRoles(Enums.Roles role)
{
  List<string> result = new List<string>();
  foreach(Roles r in Enum.GetValues(typeof(Roles))
  {
    if ((role & r) != 0) result.Add(r.ToString());
  }
}

Answer 3

Enum.Parse will handle the concatenated values outputted by ToString just fine. Proof using the Immediate window:

? System.Enum.Parse(typeof(System.AttributeTargets), "Class, Enum")
Class | Enum

(the second line is the output, which is different in the debugger/immediate window from the generic Enum.ToString() output).