Can I make this function that parses a list of enum names generic?

Question

Non Generic Version (works):

    eTargets ParseTargets(string input)
    {
        eTargets targets = eTargets.None;
        string[] items = input.Split(',');
        foreach (var item in items)
        {
            eTargets target;
            if (Enum.TryParse(item, out target))
            {
                targets |= target;
            }
            else
            {
                Logger.LogError("invalid target: " + item);
            }
        }
        return targets;
    }

Attempt at generic version (does not compile):

    T ParseNames<T>(string delimitedNames) where T : struct
    {
        T result = default(T);
        foreach (var name in delimitedNames.Split(','))
        {
            T parsed;
            if (Enum.TryParse<T>(name, out parsed)) 
                result |= (int)parsed; // ERROR: cannot convert T to int
                // result |= parsed --> operator |= cannot be applied to T and int
        }
        return (T)result;
    }

If the answer is "no", it would be helpful to understand the underlying limitation.

See http://stackoverflow.com/questions/79126/create-generic-method-constraining-t-to-an-enum for some ideas. — Henry Merriam, Jan 11 '12 at 16:44
seems like you downvoted my response as well.. I am going to delete my entry.. — MethodMan, Jan 11 '12 at 16:54

H H · Answer 1 · 2012-01-11T21:42:33.520

2

How about

T ParseNames<T>(string delimitedNames) where T : struct //, Enum
{
    return (T) Enum.Parse(typeof(T), delimitedNames);   
}

Your code already implies a 1, 2, 4, 8 numbering so the only 'gap' here is the requirement for the [Flags] attribute

edited Jan 11 '12 at 21:42

answered Jan 11 '12 at 16:48

H H

263,252
30
330
514

`Enum` is not a valid constraint on a type parameter. – vcsjones Jan 11 '12 at 16:49
yea, I fixed it in my question - sorry about that – Aaron Anodide Jan 11 '12 at 16:51
@Henk, yes the base 2 thing is implied, i should rename it ParseFlags – Aaron Anodide Jan 11 '12 at 16:51
1

you are telling me it's a built in feature that i'm trying to re-write here? – Aaron Anodide Jan 11 '12 at 16:52
@Gabriel I just learned that as well, but yes: `The value parameter contains the string representation of an enumeration member's underlying value or named constant, or a list of named constants delimited by commas (,). One or more blank spaces can precede or follow each value, name, or comma in value. If value is a list, the return value is the value of the specified names combined with a bitwise OR operation.` http://msdn.microsoft.com/en-us/library/essfb559.aspx – vcsjones Jan 11 '12 at 16:54
@Gabriel: Yes, I was wondering if this was 'just for fun' or that you missed it. – H H Jan 11 '12 at 16:56

vgru · Answer 2 · 2012-01-11T16:46:59.903

1

This should work:

static T ParseNames<T>(string delimitedNames) where T : struct
{
    int result = 0;
    foreach (var name in delimitedNames.Split(','))
    {
        result |= (int)Enum.Parse(typeof(T), name);
    }
    return (T)(object)result;
}

edited Jan 11 '12 at 16:46

answered Jan 11 '12 at 16:40

vgru

49,838
16
120
201

that results in the same error as using no cast: "operator |= cannot be applied to T and int" – Aaron Anodide Jan 11 '12 at 16:42
@Gabriel: fixed. Since `Enum.TryParse` doesn't exist in .NET 3.5, I wasn't able to test it, but you can easily modify this to your needs. – vgru Jan 11 '12 at 16:48
Apologies Groo, the down-vote was not intentional! Didn't initially realise I'd clicked it. – Wayne Cornish Jan 11 '12 at 16:52

Can I make this function that parses a list of enum names generic?

2 Answers2