public void SubstitutesCompareDefaultForNull()
{
IEqualityComparer <int> source = null;
var comparer = source.SelectEquateFrom((Person p) => p.Priority);
Assert.AreSame(EqualityCompare <int> .Default(), (comparer as SelectEqualityComparer <Person, int>).Source);
}
/// <summary>
/// Returns an equality comparer that uses a key comparer if the source comparer determines the objects are equal.
/// </summary>
/// <typeparam name="T">The type of objects being compared.</typeparam>
/// <typeparam name="TKey">The type of key objects being compared.</typeparam>
/// <param name="source">The source comparer. If this is <c>null</c>, the default comparer is used.</param>
/// <param name="selector">The key selector. May not be <c>null</c>.</param>
/// <param name="keyComparer">The key comparer. Defaults to <c>null</c>. If this is <c>null</c>, the default comparer is used.</param>
/// <param name="allowNulls">A value indicating whether <c>null</c> values are passed to <paramref name="selector"/>. If <c>false</c>, then <c>null</c> values are considered less than any non-<c>null</c> values and are not passed to <paramref name="selector"/>.</param>
/// <returns>A comparer that uses a key comparer if the source comparer determines the objects are equal.</returns>
public static IEqualityComparer <T> ThenEquateBy <T, TKey>(this IEqualityComparer <T> source, Func <T, TKey> selector, IEqualityComparer <TKey> keyComparer = null, bool allowNulls = false)
{
Contract.Requires(selector != null);
Contract.Ensures(Contract.Result <IEqualityComparer <T> >() != null);
return(source.ThenEquateBy(keyComparer.SelectEquateFrom(selector, allowNulls)));
}
/// <summary>
/// Returns an equality comparer that uses a key comparer if the source comparer determines the objects are equal.
/// </summary>
/// <typeparam name="T">The type of objects being compared.</typeparam>
/// <typeparam name="TKey">The type of key objects being compared.</typeparam>
/// <param name="source">The source comparer. If this is <c>null</c>, the default comparer is used.</param>
/// <param name="selector">The key selector. May not be <c>null</c>.</param>
/// <param name="keyComparer">The key comparer. Defaults to <c>null</c>. If this is <c>null</c>, the default comparer is used.</param>
/// <param name="specialNullHandling">A value indicating whether <c>null</c> values are passed to <paramref name="selector"/>. If <c>false</c>, then <c>null</c> values are considered less than any non-<c>null</c> values and are not passed to <paramref name="selector"/>.</param>
/// <returns>A comparer that uses a key comparer if the source comparer determines the objects are equal.</returns>
public static IFullEqualityComparer <T> ThenEquateBy <T, TKey>(this IEqualityComparer <T> source, Func <T, TKey> selector, IEqualityComparer <TKey> keyComparer = null, bool specialNullHandling = false)
{
return(source.ThenEquateBy(keyComparer.SelectEquateFrom(selector, specialNullHandling)));
}
