C# conditional using and default parameter

Question

Lets assume, we have an operation based on some file, connection, or other resource.

We need a method, which can be run with provided resource, or - if not provided - creates own:

string Foo(Resource parameter = null)
{
    if (parameter == null)
    {
        using (var res = new Resource)
        {
            res.Something();
               /*......*/
               /*......*/
               /*......*/
            return /*..........*/
        }
    }
    else 
    {
            parameter.Something();
               /*......*/
               /*......*/
               /*......*/
            return /*..........*/
    }
 }

}

It works, but this is really ugly for me. Is it a way to write it in more compact and "nice" way?

I cannot use:

string Foo(Resource parameter = null)
{
    using (var res = parameter ?? new Resource())
    {
        res.Something();
           /*......*/
           /*......*/
           /*......*/
        return /*..........*/
    }
}

as it disposes my original Resource if passed as parameter.

PS. What is proper tag for this question? #coding-style is marked as "do not use".

Answer 1

One simple approach would be to just recurse if parameter is null:

string Foo(Resource parameter = null)
{
    if (parameter == null)
    {
        using (var res = new Resource())
        {
            return Foo(res);   
        }
    }
    else 
    {
        parameter.Something();
        ...
        return ...;
    }
}

You'll only recurse once, so you don't need to worry about unbounded stacks etc.