The collections framework provides generic interfaces and implementations for common collection patterns in Delphi.

Use IEnumerable<T> when callers only need to iterate values. Use IReadOnlyCollection<T> when they also need IReadOnlyCollection<T>.Count or IReadOnlyCollection<T>.Contains. Use IList<T> for an ordered, mutable collection with indexed access.

Use the IDictionary<TKey,TValue> interface when callers need keyed lookup. Prefer the TCollections factory methods when creating collection instances.

Use TCollections.CreateObjectList<T> for a list that can own object lifetimes. When ownership is enabled, removing or deleting an object, clearing the list, or destroying the list frees the affected objects. Assigning a new value through the indexed IList<T>.Items property does not free the object being replaced.

The equality comparer passed to TCollections.CreateList<T> controls IReadOnlyCollection<T>.Contains, IList<T>.IndexOf, and ICollection<T>.Remove. It does not control sorting; pass an IComparer<T> or TComparison<T> to IList<T>.Sort for a custom order.

The equality comparer passed to TCollections.CreateDictionary<TKey,TValue> applies to keys. Dictionary value comparisons use the default equality comparer for the value type.

The collection members inherited by IDictionary<TKey,TValue> operate on TPair<TKey,TValue> values. IReadOnlyCollection<T>.Contains and ICollection<T>.Remove require both the key and value to match. ICollection<T>.Add rejects a pair whose key already exists, while assigning through IDictionary<TKey,TValue>.Items adds or replaces a value.

The IDictionary<TKey,TValue>.Keys and IDictionary<TKey,TValue>.Values properties return live read-only views that reflect later changes to the dictionary.

Choose the collection that matches the access pattern: lists for ordered traversal and indexed access, and dictionaries for keyed lookup.