The base types in MyLibrary.Types support comparison, equality, and key/value pairs used by the collection interfaces.

Use IEqualityComparer<T> when lookup operations need custom equality. Lists use it for methods such as IReadOnlyCollection<T>.Contains and IList<T>.IndexOf. Dictionaries use it for key lookup.

Use IComparer<T> or TComparison<T> when callers need custom sort order for IList<T>.Sort.

Use TPair<TKey,TValue> for dictionary enumeration and APIs that need to pass a key and value as one item.

The unit also defines common exception types used by the collection contracts, including EArgumentException, EArgumentNilException, EArgumentOutOfRangeException, EInvalidOperationException, and EKeyNotFoundException.