Question

If I have a generic method that is constrained to be type ‘int’ then surely I should be able to cast an integer to the generic T type. For example…

    public T ExampleMethod<T>(int unchanged) where T : int
    {
        return (T)unchanged;
    }

…the compiler complains that Cannot convert type ‘int’ to ‘T’ but I have a constraint indicating that the target is as integer. So surely it should work?

Update:

The actual scenario is that I want to a helper method that returns an enum value. So my ideal helper method would be more like this….

public T GetAttributeAsEnum<T>(XmlReader reader, string name) where T : enum
{
    string s = reader.GetAttribute(name);
    int i = int.Parse(s);
    return (T)i;
}

…and use it like this…

StateEnum x = GetAttributeAsEnum<StateEnum>(xmlReader, "State");
CategoryEnum y = GetAttributeAsEnum<CategoryEnum>(xmlReader, "Category");
OtherEnum z = GetAttributeAsEnum<OtherEnum>(xmlReader, "Other");

…but you cannot constrain by enum.

Answer 1

“Only class or interface could be specified as constraint.” (c) ReSharper

int (Int32) is just a struct. You can constrain that T is a struct. but you can’t use any struct as constraint.

the whole list of possible constraints you can find here – http://msdn.microsoft.com/en-us/library/d5x73970.aspx

UPD

and for Enum constraint see this question – Is there a workaround for generic type constraint of "special class" Enum in C# 3.0?