Blog
Mert Özen's blog posts on software development, backend, frontend, and DevOps.
C# 13–14 and .NET 9–10: OrderedDictionary, params Collections and More
Why Dictionary promises no order and .NET 9's generic OrderedDictionary, .NET 10's index-returning TryAdd/TryGetValue, PriorityQueue.Remove, allocation-free alternate lookup, C# 13 params collections and C# 14 extension members and span conversions.
C# 11–12 and .NET 7–8: Generic Math, Frozen and Collection Expressions
The generic sum you couldn't write in C# 10, generic math with static abstract members and INumber<T>; FrozenDictionary and FrozenSet, built once and read many times, measured with BenchmarkDotNet; square-bracket collection expressions, spread and CollectionBuilder.
Generic Variance in C#: Covariance and Contravariance (in and out)
Why can't a List<EBook> be a List<Book> when it can be an IEnumerable<Book>? The hole in array covariance, covariance with out, contravariance with in, variance in delegates, the limits of the rules and the cast trap CS0266 suggests.
Immutable Collections in C# and Choosing the Right Collection
The difference between a read-only view and real immutability, structural sharing in ImmutableList, builders, ImmutableArray versus ImmutableList measured with BenchmarkDotNet, and choosing the right collection with a complexity map.
C# Collection Interfaces: IEnumerable, ICollection, IList and yield return
What IEnumerable, ICollection, IList and the IReadOnly* interfaces promise and what they don't; why an array throws on Add, exposing an internal list safely, choosing parameter types and writing lazy iterators with yield return.
Sorted Collections in C#: SortedList, SortedDictionary, SortedSet and IComparer
A book silently lost from a SortedSet when the comparer returns zero, and the tie-breaking second criterion. SortedDictionary on a red-black tree, SortedList with two sorted arrays and when to pick which; Min, Max and the live GetViewBetween on SortedSet; IComparer, culture-sensitive string order and broken comparer traps.
C# Queue, Stack, LinkedList and PriorityQueue: Collections That Work in Order
Queue<T> for FIFO, Stack<T> for LIFO and undo, LinkedList<T> for O(1) inserts and removals through nodes, and a small LRU cache built from LinkedList and Dictionary. The .NET 6 PriorityQueue: why UnorderedItems is unordered, why it is not stable for equal priorities, a fair queue with sequence numbers, and the N most expensive books with EnqueueDequeue.
C# Dictionary and HashSet: TryGetValue, Key Equality and Comparers
How a Dictionary finds a key with GetHashCode and Equals, and why a class key without equality bloats it. The differences between Add, the indexer, TryAdd and TryGetValue, counting in a single lookup with .NET 6 CollectionsMarshal, the mutable key trap, OrdinalIgnoreCase and the Turkish I trap, ordering, and HashSet set operations.
A Guide to C# List<T>: Adding, Removing, Capacity, Sorting and Searching
Elements skipped while removing in a loop, the 'Collection was modified' error and removing correctly with RemoveAll. The array inside, Capacity growing 4-8-16-32 and EnsureCapacity; Add, Insert, Remove and equality, the Find family, Sort, BinarySearch and why Sort is not stable.
Why C# Has Generics: ArrayList, Boxing and Type Safety
The price of ArrayList storing everything as object: InvalidCastException pushed to run time, boxing of value types and eight times the memory. Type safety with List<T>, how the runtime sees generic types, and bringing old collections into the generic world with OfType and Cast.