/// <summary>
/// Returns source.Distinct(comparer) in a linqified way.
/// </summary>
public static IEnumerable <T> DistinctBy <T, TKey>(this IEnumerable <T> source,
Func <T, TKey> keySelector)
{
source.ThrowIfArgumentNull(nameof(source));
keySelector.ThrowIfArgumentNull(nameof(keySelector));
return(source.Distinct(
// calls new GenericEqualityComparer<T, TKey>(keySelector)
GenericEqualityComparer <T> .By(keySelector)
));
}
/// <summary>
/// Returns source.Except(second, comparer) in a linqified way.
/// </summary>
public static IEnumerable <T> ExceptBy <T, TKey>(this IEnumerable <T> source, IEnumerable <T> second,
Func <T, TKey> keySelector)
{
source.ThrowIfArgumentNull(nameof(source));
second.ThrowIfArgumentNull(nameof(second));
keySelector.ThrowIfArgumentNull(nameof(keySelector));
return(source.Except(second,
// calls new GenericEqualityComparer<T, TKey>(keySelector)
GenericEqualityComparer <T> .By(keySelector)
));
}