Return a List<> of active masks in C#

Question

Here's the code I'm working on (I found some of it online) and I'm trying to return a List<> of the flags that are active. Here's the code:

public static class BitMask {
        public static bool IsSet<T>(T flags, T flag) where T : struct {
            int flagsValue = (int)(object)flags;
            int flagValue = (int)(object)flag;

            return (flagsValue & flagValue) != 0;
        }

        public static void Set<T>(ref T flags, T flag) where T : struct {
            int flagsValue = (int)(object)flags;
            int flagValue = (int)(object)flag;

            flags = (T)(object)(flagsValue | flagValue);
        }

        public static void Unset<T>(ref T flags, T flag) where T : struct {
            int flagsValue = (int)(object)flags;
            int flagValue = (int)(object)flag;

            flags = (T)(object)(flagsValue & (~flagValue));
        }

        public static List<T> GetActiveMasks<T>(ref T flags) where T : struct {
            List<T> returned = new List<T>();
            foreach(T value in flags) 
                if(IsSet(flags, value))
                    returned.Add(value);

            return returned;
        }
    }

However, I'm running into this issue:

foreach statement cannot operate on variables of type 'T' because 'T' does not contain a public definition for 'GetEnumerator' (CS1579) - C:\Users\Christian\Documents\SharpDevelop Projects\OblivionScripts\OblivionScripts\Common\BitMask.cs:36,4

Could someone please nudge me in the right direction as I'm still new to C#.

This may help: http://stackoverflow.com/questions/105372/enumerate-an-enum — BJ Myers, May 06 '15 at 21:43
Your code is a very strange way to make this kind of thing generic. If you choose this path anway, use `ulong` to support larger primitives (right now, a 64-bit primitive will have its 32 most significant bits erased using this method) — Bas, May 06 '15 at 21:50

score 1 · Accepted Answer · answered May 06 '15 at 21:48

In your example, what is T going to be replaced with? Is this supposed to work with an enum that has the [Flags] attribute?

If so, then you should be able to get the code to work by writing your method like this:

    public static List<T> GetActiveMasks<T>(ref T flags) where T : struct {
        List<T> returned = new List<T>();
        foreach(T value in Enum.GetValues(typeof(T)).Cast<T>()) 
            if(IsSet(flags, value))
                returned.Add(value);

        return returned;
    }

Now, that said: note that in many such enum scenarios, the enum type has not only individual flags, but aliases and/or combined flags. Your code will detect those as being "set" as well. There's not enough context in your question to know whether this would actually be a problem, never mind how to address it correctly. I simply mention it as a possible "gotcha", in case you weren't aware.

'System.Array' does not contain a definition for 'Cast' and no extension method 'Cast' accepting a first argument of type 'System.Array' could be found (are you missing a using directive or an assembly reference?) (CS1061) - C:\Users\Christian\Documents\SharpDevelop Projects\OblivionScripts\OblivionScripts\Common\BitMask.cs:36,49 — Hobbyist, May 06 '15 at 21:56
You need to include `using System.Linq;` in your .cs file for the LINQ extensions (like `Cast()`) to work. That said, I include that only as a personal preference for clarity in the code; the `foreach` statement will implicitly cast (if possible) for you, so you could just omit that if you prefer. — Peter Duniho, May 06 '15 at 22:10

score 0 · Answer 2 · answered May 06 '15 at 21:45

0

flags needs to be some enumerable type, you probably meant:

  public static List<T> GetActiveMasks<T>(ref IEnumerable<T> flags) 
          where T : struct {
        ...
    }

answered May 06 '15 at 21:45

thumbmunkeys

20,606
8
62
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score 0 · Answer 3 · answered May 06 '15 at 21:45

The flags you pass in must be a collection of T, because T is a struct not a collection.

  public static List<T> GetActiveMasks<T>(ref IEnumerable<T> flags) where T : struct {
        List<T> returned = new List<T>();
        foreach(T value in flags) 
            if(IsSet(flags, value))
                returned.Add(value);

        return returned;
    }

score 0 · Answer 4 · answered May 06 '15 at 21:48

0

You can't iterate on a generic type. If the flags parameter were of type List<T> you'd be able to iterate on that.

public static List<T> GetActiveMasks<T>(ref List<T> flags) where T : struct

answered May 06 '15 at 21:48

TomSlick

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Return a List<> of active masks in C#

4 Answers4