How can I define a template member function in C# For instance I will fill any collection which supports an Add(...) member function, please check out the sample code below

public class CInternalCollection
{
    public static void ExternalCollectionTryOne<T<int>>(ref T<int> ext_col, int para_selection = 0)
    {
        foreach (int int_value in m_int_col)
        {
            if (int_value > para_selection)
                ext_col.Add(int_value);
        }
    }

    public static void ExternalCollectionTryTwo<T>(ref T ext_col, int para_selection = 0)
    {
        foreach (int int_value in m_int_col)
        {
            if (int_value > para_selection)
                ext_col.Add(int_value);
        }
    }


    static int[] m_int_col = { 0, -1, -3, 5, 7, -8 };
}

The ExternalCollectionTryOne<...>(...) would be the preferred kind, because the int type can be explicit defined, but results in an error:

Type parameter declaration must be an identifier not a type
The type or namespace name 'T' could not be found (are you missing a using directive or an assembly reference?)

The ExternalCollectionTryTwo<...>(...) results in an error:

'T' does not contain a definition for 'Add' and no extension method 'Add' accepting a first argument of type 'T' could be found (are you missing a using directive or an assembly reference?)...

I hope the problem is clear – any suggestions?

----------------------------- edit --------------------------

The answers with the interface ICollection<..> without a template member works fine and thanks all for this hint, but I still cannot define successfully a member template(generic) function

So a more simpler example ... how can I define this

public class CAddCollectionValues
{
    public static void AddInt<T>(ref T number, int selection)
    {
        T new_T = new T();  //this line is just an easy demonstration to get a compile error with type T  

        foreach (int i_value in m_int_col)
        {
            if (i_value > selection)
                number += i_value; //again the type T cannot be used
        }
    }

    static int[] m_int_col = { 0, -1, -3, 5, 7, -8 };
}