Generics Collections in C#

A generic collection in C# is a collection class that can store objects of a specific type, specified when the collection is created. Unlike non-generic collections, generic collections enforce type safety at compile time, preventing invalid types from being added and improve performance by eliminating the need for boxing/unboxing for value types.

Common Generic Collections in C#

1. List<T>

A dynamic array that automatically resizes as items are added. Provides indexed access, searching and sorting.

• Maintains order of elements
• Dynamic resizing
• Supports LINQ operations

2. Dictionary<TKey, TValue>

Stores key-value pairs for fast lookups by key.

• Fast retrieval using keys
• Prevents duplicate keys
• Ideal for mapping relationships

3. Queue<T>

Represents a first-in, first-out (FIFO) collection.

• Maintains insertion order
• Suitable for task scheduling or processing

4. Stack<T>

Represents a last-in, first-out (LIFO) collection.

• Last element added is the first to be removed
• Useful for undo functionality, parsing and recursion simulations

5. HashSet<T>

Stores unique elements without duplicates.

• Ensures uniqueness of elements
• Supports set operations like Union, Intersection and Difference

6. SortedList<TKey, TValue>

Stores key-value pairs sorted by key automatically.

• Maintains sorted order of keys
• Quick retrieval by key
• Useful for ordered mappings

Choosing the Right Collection

• Use List<T> for dynamic arrays and ordered lists.
• Use Dictionary<TKey, TValue> for key-value mappings with fast lookups.
• Use Queue<T> and Stack<T> when order of insertion or removal matters.
• Use HashSet<T> to ensure element uniqueness.
• Use SortedList<TKey, TValue> when you need automatically sorted key-value pairs.