public IComparer <T> CreateKeyedComparer <TKey>(Func <T, TKey> keySelector, bool nullsFirst)
{
// we want to take precedence over the new keyed comparer
IComparer <T> comparer = KeyedNullPlacementComparer <T, TKey> .GetComparer(Comparer, keySelector, nullsFirst);
return(UnkeyedNullPlacementComparer <T> .GetComparer(comparer, NullFilter.NullsFirst));
}
public IComparer <T> CreateCompoundComparer(IComparer <T> comparer)
{
CompoundComparer <T> compoundComparer = new CompoundComparer <T>();
compoundComparer.AppendComparison(Comparer);
compoundComparer.AppendComparison(comparer);
return(KeyedNullPlacementComparer <T, TKey> .GetComparer(compoundComparer.Normalize(), _keySelector, NullFilter.NullsFirst));
}
/// <summary>
/// Extends a comparer such that null values are handled up-front by treating them
/// as the largest possible value.
/// </summary>
/// <typeparam name="T">The type of the values being compared.</typeparam>
/// <typeparam name="TKey">The type of the key returned by the selector.</typeparam>
/// <param name="baseComparer">The comparer to extend to handle nulls.</param>
/// <param name="keySelector">Returns the key that will be inspected for null values.</param>
/// <returns>A new comparer that treats nulls as the largest possible value.</returns>
/// <exception cref="System.ArgumentNullException">The base comparer is null.</exception>
/// <exception cref="System.ArgumentNullException">The key selector is null.</exception>
/// <remarks>The returned comparer is guaranteed to never pass a null value to the given base comparer.</remarks>
public static IComparer <T> NullsLast <T, TKey>(this IComparer <T> baseComparer, Func <T, TKey> keySelector)
{
if (baseComparer == null)
{
throw new ArgumentNullException("baseComparer");
}
if (keySelector == null)
{
throw new ArgumentNullException("keySelector");
}
IPrecedenceEnforcer <T> previous = baseComparer as IPrecedenceEnforcer <T>;
if (previous != null)
{
return(previous.CreateKeyedComparer(keySelector, nullsFirst: false));
}
return(KeyedNullPlacementComparer <T, TKey> .GetComparer(baseComparer, keySelector, nullsFirst : false));
}
public IComparer <T> CreateKeyedComparer <TOtherKey>(Func <T, TOtherKey> keySelector, bool nullsFirst)
{
// we don't know if the key selector is identical, so we must wrap ourselves
return(KeyedNullPlacementComparer <T, TOtherKey> .GetComparer(this, keySelector, nullsFirst));
}