How to refactor these functions which have one line difference

Question

I have 3 functions where the only difference in is the values I point out with comment

//-- point of difference

The majority of the function is the same across all three. The "DRY" factor is haunting my sleep :). I was wondering; can these could be merged easily and readably?

I have had situations like this before and I am hoping to learn something here.

private string RenderRequestType(string render, NameValueCollection nvp, string prefix, string regexWild, string suffix)
{
    string regex = prefix + regexWild + suffix;

    MatchCollection matches = Regex.Matches(render, regex);

    foreach (Match match in matches)
    {
        foreach (Capture capture in match.Captures)
        {
            string name = capture.Value.Replace(prefix, "", StringComparison.CurrentCultureIgnoreCase).Replace(suffix, "", StringComparison.CurrentCultureIgnoreCase);

            //-- point of difference
            string value = nvp[name];

            render = render.Replace(capture.Value, value);
        }
    }

    return render;
}

private string RenderSessionType(string render, HttpContext httpContext, string prefix, string regexWild, string suffix)
{
    string regex = prefix + regexWild + suffix;

    MatchCollection matches = Regex.Matches(render, regex);

    foreach (Match match in matches)
    {
        foreach (Capture capture in match.Captures)
        {
            string name = capture.Value.Replace(prefix, "", StringComparison.CurrentCultureIgnoreCase).Replace(suffix, "", StringComparison.CurrentCultureIgnoreCase);

            //-- point of difference
            object session = httpContext.Session[name];
            string value = (session != null ? session.ToString() : "");

            render = render.Replace(capture.Value, value);
        }
    }

    return render;
}

private string RenderCookieType(string render, HttpContext httpContext, string prefix, string regexWild, string suffix)
{
    string regex = prefix + regexWild + suffix;

    MatchCollection matches = Regex.Matches(render, regex);

    foreach (Match match in matches)
    {
        foreach (Capture capture in match.Captures)
        {
            string name = capture.Value.Replace(prefix, "", StringComparison.CurrentCultureIgnoreCase).Replace(suffix, "", StringComparison.CurrentCultureIgnoreCase);

            //-- point of difference
            HttpCookie cookie = httpContext.Request.Cookies[name];
            string value = (cookie != null ? cookie.Value : "");

            render = render.Replace(capture.Value, value);
        }
    }

    return render;
}

Answer 1

You could modify the function to take a Func<string, string> to do the lookup:

private string RenderType(string render, Func<string, string> lookupFunc, string prefix, string regexWild, string suffix)
{
    string regex = prefix + regexWild + suffix;

    MatchCollection matches = Regex.Matches(render, regex);

    foreach (Match match in matches)
    {
        foreach (Capture capture in match.Captures)
        {
            string name = capture.Value.Replace(prefix, "", StringComparison.CurrentCultureIgnoreCase).Replace(suffix, "", StringComparison.CurrentCultureIgnoreCase);

            //-- point of difference
            string value = lookupFunc(name);

            render = render.Replace(capture.Value, value);
        }
    }

    return render;
}

Then write your functions in terms of this one, e.g.:

private string RenderRequestType(string render, NameValueCollection nvp, string prefix, string regexWild, string suffix)
{
    return RenderType(render, name => nvp[name], prefix, regexWild, suffix);
}

Answer 2

Pass in a Func<string, string> to get the value associated with a given name. In the first case that would just use nvp's indexer; in the second it would use the session. You could either use separate methods to create the delegates, or lambda expressions. (I'd definitely use a lambda expression for the first one; I might use a separate method for the second.)