System.Collections.Generic Namespace

Contains interfaces and classes that define generic collections, which allow users to create strongly typed collections that provide better type safety and performance than non-generic strongly typed collections.

Classes

CollectionExtensions	Provides extension methods for generic collections.
Comparer<T>	Provides a base class for implementations of the IComparer<T> generic interface.
Dictionary<TKey,TValue>.KeyCollection	Represents the collection of keys in a Dictionary<TKey,TValue>. This class cannot be inherited.
Dictionary<TKey,TValue>.ValueCollection	Represents the collection of values in a Dictionary<TKey,TValue>. This class cannot be inherited.
Dictionary<TKey,TValue>	Represents a collection of keys and values.
EqualityComparer<T>	Provides a base class for implementations of the IEqualityComparer<T> generic interface.
HashSet<T>	Represents a set of values.
KeyedByTypeCollection<TItem>	Provides a collection whose items are types that serve as keys.
KeyNotFoundException	The exception that is thrown when the key specified for accessing an element in a collection does not match any key in the collection.
KeyValuePair	Creates instances of the KeyValuePair<TKey,TValue> struct.
LinkedList<T>	Represents a doubly linked list.
LinkedListNode<T>	Represents a node in a LinkedList<T>. This class cannot be inherited.
List<T>	Represents a strongly typed list of objects that can be accessed by index. Provides methods to search, sort, and manipulate lists.
PriorityQueue<TElement,TPriority>.UnorderedItemsCollection	Enumerates the contents of a PriorityQueue<TElement,TPriority>, without any ordering guarantees.
PriorityQueue<TElement,TPriority>	Represents a collection of items that have a value and a priority. On dequeue, the item with the lowest priority value is removed.
Queue<T>	Represents a first-in, first-out collection of objects.
ReferenceEqualityComparer	An IEqualityComparer<T> that uses reference equality (ReferenceEquals(Object, Object)) instead of value equality (Equals(Object)) when comparing two object instances.
SortedDictionary<TKey,TValue>.KeyCollection	Represents the collection of keys in a SortedDictionary<TKey,TValue>. This class cannot be inherited.
SortedDictionary<TKey,TValue>.ValueCollection	Represents the collection of values in a SortedDictionary<TKey,TValue>. This class cannot be inherited.
SortedDictionary<TKey,TValue>	Represents a collection of key/value pairs that are sorted on the key.
SortedList<TKey,TValue>	Represents a collection of key/value pairs that are sorted by key based on the associated IComparer<T> implementation.
SortedSet<T>	Represents a collection of objects that is maintained in sorted order.
Stack<T>	Represents a variable size last-in-first-out (LIFO) collection of instances of the same specified type.
SynchronizedCollection<T>	Provides a thread-safe collection that contains objects of a type specified by the generic parameter as elements.
SynchronizedKeyedCollection<K,T>	Provides a thread-safe collection that contains objects of a type specified by a generic parameter and that are grouped by keys.
SynchronizedReadOnlyCollection<T>	Provides a thread-safe, read-only collection that contains objects of a type specified by the generic parameter as elements.

Structs

Dictionary<TKey,TValue>.Enumerator	Enumerates the elements of a Dictionary<TKey,TValue>.
Dictionary<TKey,TValue>.KeyCollection.Enumerator	Enumerates the elements of a Dictionary<TKey,TValue>.KeyCollection.
Dictionary<TKey,TValue>.ValueCollection.Enumerator	Enumerates the elements of a Dictionary<TKey,TValue>.ValueCollection.
HashSet<T>.Enumerator	Enumerates the elements of a HashSet<T> object.
KeyValuePair<TKey,TValue>	Defines a key/value pair that can be set or retrieved.
LinkedList<T>.Enumerator	Enumerates the elements of a LinkedList<T>.
List<T>.Enumerator	Enumerates the elements of a List<T>.
PriorityQueue<TElement,TPriority>.UnorderedItemsCollection.Enumerator	Enumerates the element and priority pairs of a PriorityQueue<TElement,TPriority>, without any ordering guarantees.
Queue<T>.Enumerator	Enumerates the elements of a Queue<T>.
SortedDictionary<TKey,TValue>.Enumerator	Enumerates the elements of a SortedDictionary<TKey,TValue>.
SortedDictionary<TKey,TValue>.KeyCollection.Enumerator	Enumerates the elements of a SortedDictionary<TKey,TValue>.KeyCollection.
SortedDictionary<TKey,TValue>.ValueCollection.Enumerator	Enumerates the elements of a SortedDictionary<TKey,TValue>.ValueCollection.
SortedSet<T>.Enumerator	Enumerates the elements of a SortedSet<T> object.
Stack<T>.Enumerator	Enumerates the elements of a Stack<T>.

Interfaces

IAsyncEnumerable<T>	Exposes an enumerator that provides asynchronous iteration over values of a specified type.
IAsyncEnumerator<T>	Supports a simple asynchronous iteration over a generic collection.
ICollection<T>	Defines methods to manipulate generic collections.
IComparer<T>	Defines a method that a type implements to compare two objects.
IDictionary<TKey,TValue>	Represents a generic collection of key/value pairs.
IEnumerable<T>	Exposes the enumerator, which supports a simple iteration over a collection of a specified type.
IEnumerator<T>	Supports a simple iteration over a generic collection.
IEqualityComparer<T>	Defines methods to support the comparison of objects for equality.
IList<T>	Represents a collection of objects that can be individually accessed by index.
IReadOnlyCollection<T>	Represents a strongly-typed, read-only collection of elements.
IReadOnlyDictionary<TKey,TValue>	Represents a generic read-only collection of key/value pairs.
IReadOnlyList<T>	Represents a read-only collection of elements that can be accessed by index.
IReadOnlySet<T>	Provides a readonly abstraction of a set.
ISet<T>	Provides the base interface for the abstraction of sets.

Remarks

Many of the generic collection types are direct analogs of nongeneric types. Dictionary<TKey,TValue> is a generic version of Hashtable; it uses the generic structure KeyValuePair<TKey,TValue> for enumeration instead of DictionaryEntry. List<T> is a generic version of ArrayList. There are generic Queue<T> and Stack<T> classes that correspond to the nongeneric versions. There are generic and nongeneric versions of SortedList<TKey,TValue>. Both versions are hybrids of a dictionary and a list. The SortedDictionary<TKey,TValue> generic class is a pure dictionary and has no nongeneric counterpart. The LinkedList<T> generic class is a true linked list and has no nongeneric counterpart.

See also

• Generic Collections in .NET