Use of Distinct with list of custom objects

Question

How can I make the Distinct() method work with a list of custom object (Href in this case), here is what the current object looks like:

public class Href : IComparable, IComparer<Href>
{
    public Uri URL { get; set; }
    public UrlType URLType { get; set; }

    public Href(Uri url, UrlType urltype)
    {
        URL = url;
        URLType = urltype;
    }


    #region IComparable Members

    public int CompareTo(object obj)
    {
        if (obj is Href)
        {
            return URL.ToString().CompareTo((obj as Href).URL.ToString());
        }
        else
            throw new ArgumentException("Wrong data type.");
    }

    #endregion

    #region IComparer<Href> Members

    int IComparer<Href>.Compare(Href x, Href y)
    {
        return string.Compare(x.URL.ToString(), y.URL.ToString());
    }

    #endregion
}

Answer 1

You need to override Equals and GetHashCode.

GetHashCode should return the same value for all instances that are considered equal.

For example:

public override bool Equals(object obj) { 
    Href other = obj as Href;
    return other != null && URL.Equals(other.URL);
} 

public override int GetHashCode() { 
    return URL.GetHashCode();
} 

Since .Net's Uri class overrides GetHashCode, you can simply return the URL's hashcode.

Answer 2

You could grab a copy of aku's comparer (beware of the GetHashCode implementation however), and then write something like this

hrefList.Distinct(new Comparer<Href>((h1,h2)=>h1.URL==h2.URL))