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(UnkeyedNullPlacementComparer <T> .GetComparer(compoundComparer.Normalize(), NullFilter.NullsFirst));
}
public IComparer <T> CreateUnkeyedComparer(bool nullsFirst)
{
// we're duplicating ourselves
if (nullsFirst == NullFilter.NullsFirst)
{
return(this);
}
// we're replacing ourselves with another top-level comparer with a different sort order
return(UnkeyedNullPlacementComparer <T> .GetComparer(Comparer, nullsFirst));
}
/// <summary>
/// Extends a non-nullable comparer to work against nullable values by specifying
/// nulls should be treated as the largest possible value.
/// </summary>
/// <typeparam name="T">The non-nullable type being compared by the base comparer.</typeparam>
/// <param name="baseComparer">The comparer used to compare non-nullable values.</param>
/// <returns>A new comparer capable of comparing a nullable version fo the value type.</returns>
/// <exception cref="System.ArgumentNullException">The base comparer is null.</exception>
public static IComparer <T?> ToNullableComparer <T>(this IComparer <T> baseComparer)
where T : struct
{
if (baseComparer == null)
{
throw new ArgumentNullException("baseComparer");
}
IComparer <T?> uncheckedComparer = new UncheckedNullableComparer <T>(baseComparer);
return(UnkeyedNullPlacementComparer <T?> .GetComparer(uncheckedComparer, nullsFirst : true));
}
/// <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>
/// <param name="baseComparer">The comparer to extend to handle nulls.</param>
/// <returns>A new comparer that treats nulls as the largest possible value.</returns>
/// <exception cref="System.ArgumentNullException">The base comparer 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>(this IComparer <T> baseComparer)
{
if (baseComparer == null)
{
throw new ArgumentNullException("baseComparer");
}
IPrecedenceEnforcer <T> previous = baseComparer as IPrecedenceEnforcer <T>;
if (previous != null)
{
return(previous.CreateUnkeyedComparer(nullsFirst: false));
}
return(UnkeyedNullPlacementComparer <T> .GetComparer(baseComparer, nullsFirst : false));
}
public IComparer <T> CreateUnkeyedComparer(bool nullsFirst)
{
// top-level comparers should be evaluated before keyed comparers
return(UnkeyedNullPlacementComparer <T> .GetComparer(this, nullsFirst));
}
