CODEWITHSUNDEEP
c#casting
Robby Smet
Robby Smet

Reputation: 4661

Cannot implicitly convert type with extension method

I have a extension method for an enum

public static IEnumerable<T> GetFlags<T>(this T value) where T : struct
    {
        CheckIsEnum<T>(true);
        foreach (T flag in Enum.GetValues(typeof(T)).Cast<T>())
        {
            if (value.IsFlagSet(flag))
                yield return flag;
        }
    }

I try to get the result like this:

Zone_Status_ZoneConditionFlagEnum flags = (Zone_Status_ZoneConditionFlagEnum)flagsRaw;

List<Zone_Status_ZoneConditionFlagEnum> ZoneConditionFlags_List = (List<Zone_Status_ZoneConditionFlagEnum>)flags.GetFlags();

But I get 

NX584(NX584Test)->Error parsing message: Cannot implicitly convert type [Digicom.NX584Engine.Messages.Zone_Status_ZoneConditionFlagEnum] to System.Collections.Generic.List`1[Digicom.NX584Engine.Messages.Zone_Status_ZoneConditionFlagEnum].

Upvotes: 2

Views: 330

Answers (3)

Marc Gravell
Marc Gravell

Reputation: 1062512

The first issue here is that a sequence is different to a list; if you need a list, either return a list, or add .ToList() after GetFlags(), i.e. 

var ZoneConditionFlags_List = flags.GetFlags().ToList();

However, the bigger problem is that you can't use that IsFlagSet in that generic context; that method is not defined for an arbitrary T : struct.

Personally, I think you'd be better just to treat it as a [Flags] enum throughout; I assume you have existing code that wants a list rather than a single value?

Upvotes: 1

Lasse V. Karlsen
Lasse V. Karlsen

Reputation: 391276

GetFlags returns an IEnumerable<T>, not a List<T>, you cannot cast here.

You should, however, be able to construct a list from the results:

List<Zone_Status_ZoneConditionFlagEnum> ZoneConditionFlags_List = flags.GetFlags().ToList();

However, the error does not match the code here exactly, it should complain about an IEnumerable not be able to be cast, but instead it says the enum type. Are you sure this is the right code?

Upvotes: 0

Jon Skeet
Jon Skeet

Reputation: 1499790

It's not clear to me why you're getting that error - but you can't cast the result of GetFlags<T> to a List<T>, because it doesn't return a List<T>. The simplest fix would be:

var ZoneConditionFlags_List = flags.GetFlags().ToList();

If that doesn't work, please give the new error message.

Alternatively, you could change GetFlags so it actually returned a List<T> rather than using an iterator block.

Upvotes: 2

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