public static IEnumerable<TSource> Distinct<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> selector)
{
    return source.Distinct(new SelectorEqualityComparer<TSource, TKey>(selector));
}

public static IEnumerable<TSource> Distinct<TSource>(this IEnumerable<TSource> source, Func<TSource, TSource, bool> predicate)
{
    return source.Distinct(new PredicateEqualityComparer<TSource>(predicate));
}

[Serializable]
public class SelectorEqualityComparer<TSource, Tkey> : EqualityComparer<TSource>
{
    private Func<TSource, Tkey> selector;
 
    public SelectorEqualityComparer(Func<TSource, Tkey> selector)
        : base()
    {
        this.selector = selector;
    }

[Serializable]
public class PredicateEqualityComparer<T> : EqualityComparer<T>
{
    private Func<T, T, bool> predicate;
 
    public PredicateEqualityComparer(Func<T, T, bool> predicate)
        : base()
    {
        this.predicate = predicate;
    }