SystemCollectionsGeneric

System.Collections.Generic is a namespace in the .NET platform that contains generic collection types and interfaces. It provides type-safe, high-performance containers that can store any reference or value type, with compile-time checking and reduced boxing for value types. The types in this namespace complement non-generic collections by offering strongly typed alternatives and support for iteration through foreach and integration with LINQ through IEnumerable<T>.

Key interfaces include IEnumerable<T>, IEnumerator<T>, ICollection<T>, IList<T>, IDictionary<TKey,TValue>, and ISet<T>, as well as their read-only variants IReadOnlyList<T> and IReadOnlyDictionary<TKey,TValue>, and comparers like IComparer<T> and IEqualityComparer<T>. These interfaces define semantics for counting, enumeration, indexing and equality, enabling generic APIs that work with multiple concrete collection types.

Common concrete types include List<T> (dynamic array), Dictionary<TKey,TValue> (hash table), LinkedList<T>, Queue<T>, Stack<T>, HashSet<T>, SortedSet<T>, SortedDictionary<TKey,TValue>, and SortedList<TKey,TValue>. These classes cover common use cases such as dynamic sequences, key/value maps, and ordered collections.

Notes: instances are not thread-safe by default; concurrent access requires synchronization or use of the System.Collections.Concurrent namespace. Capacity and initial sizing can affect performance. The namespace is part of .NET Framework, .NET Core, and .NET, and remains foundational for generic collection usage across versions.