Make a method generic
<p>I have a method that extract days names from a particular object, 
like this: </p>

<pre><code>private string ExtractWeekDayNames(FiscalReceipt fiscalReceipt)
    {
        string retVal = "";

        Dictionary&lt;string, bool&gt; WeekDays = 
            new Dictionary&lt;string, bool&gt;() {
                                            { "Sun", fiscalReceipt.Sunday },
                                            { "Mon", fiscalReceipt.Monday },
                                            { "Tue", fiscalReceipt.Tuesday },
                                            { "Wed", fiscalReceipt.Wednesday },
                                            { "Thu", fiscalReceipt.Thursday },
                                            { "Fri", fiscalReceipt.Friday },
                                            { "Sat", fiscalReceipt.Saturday }
                                            };


        //Find week days
        foreach (var item in WeekDays)
        {
            if (item.Value == true)
                retVal += item.Key + ",";
        }

        if (!string.IsNullOrEmpty(retVal))
            retVal = retVal.Substring(0, retVal.Length - 1);

        return retVal;

    }
</code></pre>

<p>I also have a similar method that performs the same operations 
but having a different type of parameter, like: </p>

<pre><code>private string ExtractWeekDayNames(NonFiscalReceipt nonFiscalReceipt)
{
    ...
}
</code></pre>

<p>Also the NonFiscalReceipt has the properties Sunday, Monday, etc. </p>

<p>How can I substitute these 2 methods with just one?</p>