Cannot define T in C#

Question

Any clue how to define T in this code?

 public static T ToEnum<T>(this string value, T defaultValue)
        {
            if (string.IsNullOrEmpty(value))
            {
                return defaultValue;
            }

            T result;
            return Enum.TryParse<T>(value, true, out result) ? result : defaultValue;
        }

Severity Code Description Project File Line Error CS0453 The type 'T' must be a non-nullable value type in order to use it as parameter 'TEnum' in the generic type or method 'Enum.TryParse(string, bool, out TEnum)'

@PetSerAl Please write out the whole code like an answer. Thank you! — NoWar, Jan 15 '16 at 18:40
Please read [ask]. If you can define "this", you can search for it. Do you want a "generic type constraint for an enum"? — CodeCaster, Jan 15 '16 at 18:43

Felipe Oriani · Accepted Answer · 2016-01-15T19:14:50.740

4

Try using a constraint to have a value type which is a struct, for sample:

public static T ToEnum<T>(this string value, T defaultValue)
      where T : struct 
{
    if (string.IsNullOrEmpty(value))
    {
        return defaultValue;
    }

    T result;
    return Enum.TryParse<T>(value, true, out result) ? result : defaultValue;
}

I haven't tested it.

edited Jan 15 '16 at 19:14

answered Jan 15 '16 at 18:41

Felipe Oriani

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Beat me by a second! – Camilo Terevinto Jan 15 '16 at 18:41
It gives the error `Severity Code Description Project File Line Error CS0451 The 'new()' constraint cannot be used with the 'struct' constraint ` – NoWar Jan 15 '16 at 18:42
1

Try using the ´Enum` as a constraint! – Felipe Oriani Jan 15 '16 at 18:42
1

Just remove `, new()` OP, an enum cannot be "new" – Camilo Terevinto Jan 15 '16 at 18:43
2

`where T : Enum` is not a valid template constraint in C#. – Rob Jan 15 '16 at 18:49

Cannot define T in C#

1 Answers1