Generic IEqualityComparer and GetHashCode

Question

Being somewhat lazy about implementing lots of IEqualityComparers, and given that I couldn\'t easily edit class implementations of object being compared, I went with the fol

Answer 1

Found this one on CodeProject - A Generic IEqualityComparer for Linq Distinct() nicely done.

Use case:

IEqualityComparer c =  new PropertyComparer("Name");
IEnumerable distinctEmails = collection.Distinct(c); 

Generic IEqualityComparer

public class PropertyComparer : IEqualityComparer
{
    private PropertyInfo _PropertyInfo;

    /// 

    /// Creates a new instance of PropertyComparer.
    /// 
    /// The name of the property on type T 
    /// to perform the comparison on.
    public PropertyComparer(string propertyName)
    {
        //store a reference to the property info object for use during the comparison
        _PropertyInfo = typeof(T).GetProperty(propertyName, 
    BindingFlags.GetProperty | BindingFlags.Instance | BindingFlags.Public);
        if (_PropertyInfo == null)
        {
            throw new ArgumentException(string.Format("{0} 
        is not a property of type {1}.", propertyName, typeof(T)));
        }
    }

    #region IEqualityComparer Members

    public bool Equals(T x, T y)
    {
        //get the current value of the comparison property of x and of y
        object xValue = _PropertyInfo.GetValue(x, null);
        object yValue = _PropertyInfo.GetValue(y, null);

        //if the xValue is null then we consider them equal if and only if yValue is null
        if (xValue == null)
            return yValue == null;

        //use the default comparer for whatever type the comparison property is.
        return xValue.Equals(yValue);
    }

    public int GetHashCode(T obj)
    {
        //get the value of the comparison property out of obj
        object propertyValue = _PropertyInfo.GetValue(obj, null);

        if (propertyValue == null)
            return 0;

        else
            return propertyValue.GetHashCode();
    }

    #endregion
}