The journey of every round

Use Memory<byte> and ArrayPool<byte>.Shared to read a file in 4KB chunks without re-allocating buffers per iteration. No async.

Convert a Guid to a base64 url-safe string (no padding, '+' → '-', '/' → '_') and back. Round-trip test.

Use a yield return iterator method to lazily enumerate Fibonacci numbers up to a given limit. Show the caller using foreach with a take of 10.

Demonstrate await on Task.Delay inside an async method that returns Task<int>. Show calling it twice in parallel via Task.WhenAll.

Write a custom equality comparer (IEqualityComparer<Person>) that treats two Person records as equal when Email lowercased matches. Include GetHashCode.

Implement nullable reference type annotations on a 'Person' class with FirstName (non-null), MiddleName (nullable), LastName (non-null). Show a constructor that enforces non-nullness.

Show typeof(T) vs T.GetType() inside a generic method. Demonstrate typeof(T) is the static declared type and GetType() is the runtime type for boxed values.

Use Random.Shared to pick a random element from a List<T> in a generic Pick<T>(List<T>) extension method.

Use DateTime.UtcNow plus a TimeSpan to compute a deadline 7 business days from now, skipping Saturday and Sunday.

Write a Regex that matches IPv4 addresses in the form '1.2.3.4' (each octet 0–255). Use Regex.Match on a sample string.

Define an interface IShape with one method Area(). Implement Circle and Rectangle records. Show a List<IShape> being summed via LINQ Sum.

Write an extension method on IEnumerable<T> called 'Chunk(int size)' that yields IEnumerable<T> chunks of the given size. Do not call the built-in Enumerable.Chunk.

Use StringBuilder to format a CSV row from an array of object?, treating null as empty. Escape any commas in values by wrapping in quotes.

Implement IComparable<T> on a 'SemVer' struct (Major, Minor, Patch). Show sorting a List<SemVer>.

Write a ReadOnlySpan<byte>-based UTF-8 BOM check: return true if the span starts with the bytes 0xEF 0xBB 0xBF.

Convert a List<string> to a Dictionary<string,int> mapping each string to its length, using LINQ's ToDictionary.

Demonstrate pattern matching against a tuple (int x, int y) to classify a point as 'Origin', 'OnXAxis', 'OnYAxis', or 'Inside' the unit square.

Write a generic method 'MaxBy<T,TKey>(IEnumerable<T>, Func<T,TKey>) where TKey:IComparable<TKey>' that returns the element with the maximum key.

Define an enum with [Flags] for ANSI text styles (Bold=1, Italic=2, Underline=4, Strike=8). Show combining values and testing with HasFlag.

Write a using-block over a StreamReader that reads each line and counts occurrences of the word 'foo'. No async.

Use a Span<char> to parse an integer from a string slice without allocating. Compare to int.Parse(string) qualitatively.

Write a switch expression that maps an int status code (200, 301, 404, 500) to a string label. Use the 'when' clause for the 5xx range.

Given a List<int>, return a new list containing only the even numbers, each squared, using LINQ method syntax (Where + Select). One line.

Implement a record type 'Money' with Amount (decimal) and Currency (string). Override ToString to print '€100.00 EUR'-style and show value equality with two instances.