Gist related to my "Delegate your equality comparisons" blogpost on http://marcofranssen.nl

CompareExtensions.cs

public static class CompareExtensions
{
    public static IEnumerable<T> Distinct<T>(this IEnumerable<T> items, Func<T, T, bool> equals, Func<T, int> hashCode)
    {
        return items.Distinct(new DelegateEqualityComparer<T>(equals, hashCode));
    }

    public static IEnumerable<T> Distinct<T>(this IEnumerable<T> items, Func<T, T, bool> equals)
    {
        return items.Distinct(new DelegateEqualityComparer<T>(equals, null));
    }
}

DelegateEqualityComparer.cs

public class DelegateEqualityComparer<T> : IEqualityComparer<T>
{
    private readonly Func<T, T, bool> _equals;
    private readonly Func<T, int> _hashCode;
    public DelegateEqualityComparer(Func<T, T, bool> equals, Func<T, int> hashCode)
    {
        _equals = equals;
        _hashCode = hashCode;
    }

    public bool Equals(T x, T y)
    {
        return _equals(x, y);
    }

    public int GetHashCode(T obj)
    {
        if (_hashCode != null)
            return _hashCode(obj);
        return obj.GetHashCode();
    }
}

PersonLastNameEqualityComparer.cs

public class PersonLastNameEqualityComparer : IEqualityComparer<Person>
{
    public bool Equals(Person x, Person y)
    {
        return x.LastName == y.LastName;
    }

    public int GetHashCode(Person obj)
    {
        return obj.LastName.GetHashCode();
    }
}

ProductIdEqualityComparer.cs

public class ProductIdEqualityComparer : IEqualityComparer<Product>
{
    public bool Equals(Product x, Product y)
    {
        return x.Id == y.Id;
    }

    public int GetHashCode(Product obj)
    {
        return obj.Id.GetHashCode();
    }
}

ProductPriceEqualityComparer.cs

public class ProductPriceEqualityComparer : IEqualityComparer<Product>
{
    public bool Equals(Product x, Product y)
    {
        return x.Price == y.Price;
    }

    public int GetHashCode(Product obj)
    {
        return obj.Price.GetHashCode();
    }
}

UsageExample.cs

_products.Distinct((x, y) => x.Id == y.Id, x => x.Id.GetHashCode());
_products.Distinct((x, y) => x.Price == y.Price, x => x.Price.GetHashCode());
_persons.Distinct((x, y) => x.LastName == y.LastName, x => x.LastName.GetHashCode());
_persons.Distinct((x, y) => x.FirstName == y.FirstName, x => x.FirstName.GetHashCode());
_persons.Distinct((x, y) => x.Address.City == y.Address.City, x => x.Address.City.GetHashCode());