C# Code Examples by Khalid Abuhakmeh

Switch expressions — Tip #010

Tue, 03 Nov 2026 05:00:00 GMT

A switch expression returns a value directly, with no case labels or temp variable.

A switch expression returns a value directly, with no case labels or temp variable. Pattern match with a switch expression: every arm returns a value, and _ catches the rest. It is available since C# 8. The key line is `Species.Cat => "Purrr..."` in `switch.cs`.

foreach (var species in Enum.GetValues<Species>())
{
    Console.WriteLine(species switch
    {
        Species.Cat => "Purrr...",
        Species.Dog => "Woof!",
        _ => "*Cthulhu noises*",
    });
}

enum Species { Unknown, Cat, Dog }

*Cthulhu noises*
Purrr...
Woof!

Sum per group with AggregateBy — Tip #009

Tue, 03 Nov 2026 05:00:00 GMT

AggregateBy groups and aggregates in one pass. No GroupBy + Select + Sum pipeline.

AggregateBy groups and aggregates in one pass. No GroupBy + Select + Sum pipeline. Total weight per species without GroupBy().Select(Sum): .NET 9 AggregateBy groups and folds in one pass. It is available since .NET 9. The key line is `var totals = pets.AggregateBy(` in `aggregateby.cs`. Run it and the output reads `Cat: 35, Dog: 259`.

Pet[] pets = [
    new(Species.Cat, 20), new(Species.Dog, 60),
    new(Species.Dog, 199), new(Species.Cat, 15),
];

var totals = pets.AggregateBy(
    p => p.Species, 0, (sum, p) => sum + p.Weight);

foreach (var (species, weight) in totals)
    Console.WriteLine($"{species}: {weight}");

record Pet(Species Species, int Weight = 0);
enum Species { Unknown, Cat, Dog }

Cat: 35
Dog: 259

Culture-aware interpolation — Tip #008

Tue, 03 Nov 2026 05:00:00 GMT

FormattableString keeps the values and :C format for rendering with a chosen culture. The fr-FR result has a non-breaking space before €.

FormattableString keeps the values and :C format for rendering with a chosen culture. The fr-FR result has a non-breaking space before €. Interpolate once, format later: a FormattableString keeps the :C format so you render it with any CultureInfo. It is available since C# 6. The key line is `FormattableString text = $"{price:C}"` in `formats.cs`. Run it and the output reads `$100.00, 100,00 €`.

using System.Globalization;

var price = 100m;
FormattableString text = $"{price:C}";

var usa = CultureInfo.GetCultureInfo("en-US");
var euro = CultureInfo.GetCultureInfo("fr-FR");

Console.WriteLine(text.ToString(usa));
Console.WriteLine(text.ToString(euro));

$100.00
100,00 €

Method groups in LINQ — Tip #007

Tue, 03 Nov 2026 05:00:00 GMT

When a lambda only forwards its argument, pass the method name. Same result, less noise.

When a lambda only forwards its argument, pass the method name. Same result, less noise. It is available since C# 2. The key line is `var verbose = cart.Select(x => Display(x)).ToList()` in `methodgroup.cs`. Run it and the output reads `<APPLE>, <PEAR>, <FIG>, True`.

string[] cart = ["apple", "pear", "fig"];

var verbose = cart.Select(x => Display(x)).ToList();
var concise = cart.Select(Display).ToList();

Console.WriteLine(string.Join(", ", concise));
Console.WriteLine(verbose.SequenceEqual(concise));

static string Display(string s) => $"<{s.ToUpper()}>";

<APPLE>, <PEAR>, <FIG>
True

Chain lambdas on one delegate — Tip #006

Tue, 03 Nov 2026 05:00:00 GMT

Delegates are multicast: += chains lambdas and one call runs them all, in order.

Delegates are multicast: += chains lambdas and one call runs them all, in order. It is available since C# 3. The key line is `hello += () => Console.Write("World, ")` in `lambdas.cs`. Run it and the output reads `Hello World, .NET & Khalid`.

Action hello = () => Console.Write("Hello ");
hello += () => Console.Write("World, ");
hello += () => Console.WriteLine(".NET & Khalid");
hello();

Hello World, .NET & Khalid

Union types in C# 15 — Tip #005

Tue, 03 Nov 2026 05:00:00 GMT

A union declares a closed set of case types. The compiler warns (CS8509) when a switch misses a case.

A union declares a closed set of case types. The compiler warns (CS8509) when a switch misses a case. C# 15 ships union types in .NET 11. Declare union Pet(Cat, Dog, Bird) and the compiler checks that your switch covers every case. Drop Bird and you get CS8509 "'Bird' is not covered". Run it with the .NET 11 SDK. It is new in C# 15. The key line is `union Pet(Cat, Dog, Bird)` in `pets.cs`. Run it and the output reads `Rex says woof`.

Pet pet = new Dog("Rex");
var sound = pet switch
{
    Cat c => $"{c.Name} says meow",
    Dog d => $"{d.Name} says woof",
    Bird b => $"{b.Name} says tweet",
};
Console.WriteLine(sound);

record Cat(string Name);
record Dog(string Name);
record Bird(string Name);
union Pet(Cat, Dog, Bird);

Rex says woof

Copy a record, change one thing — Tip #004

Tue, 03 Nov 2026 05:00:00 GMT

A with expression copies a record and changes only the properties you name. Records compare by value.

A with expression copies a record and changes only the properties you name. Records compare by value. It is available since C# 9. The key line is `var nicole = khalid with { Name = "Nicole" }` in `records.cs`. Run it and the output reads `Person { Name = Nicole, Planet = Earth }, False`.

var khalid = new Person("Khalid", "Earth");
var nicole = khalid with { Name = "Nicole" };

Console.WriteLine(nicole);
Console.WriteLine(khalid == nicole);

record Person(string Name, string Planet);

Person { Name = Nicole, Planet = Earth }
False

Make big numbers readable — Tip #003

Tue, 03 Nov 2026 05:00:00 GMT

The compiler ignores underscores in numeric literals. They work in hex and binary too.

The compiler ignores underscores in numeric literals. They work in hex and binary too. How many zeroes? `1_000_000_000` vs `1000000000`. It is available since C# 7. The key line is `var easyBillion = 1_000_000_000` in `numbers.cs`. It fits in 12 lines; run it with `dotnet run numbers.cs`.

// how many zeroes is a billion?
var billion = 1000000000;

// oh! nine zeroes.
var easyBillion = 1_000_000_000;
Console.WriteLine(billion == easyBillion);

// works with hex and binary too
var color = 0xFF_EF_44_44;
var flags = 0b1010_0101;
Console.WriteLine(color.GetType());
Console.WriteLine(flags);

True
System.UInt32
165

Filter exceptions with when — Tip #002

Tue, 03 Nov 2026 05:00:00 GMT

A when filter decides whether a catch block handles the exception. If false, the exception keeps propagating.

A when filter decides whether a catch block handles the exception. If false, the exception keeps propagating. Everything else propagates with its stack trace intact. On .NET 8+, filter on `ex.HttpRequestError`. It is available since C# 6. The key line is `when (ex.StatusCode == HttpStatusCode.NotFound)` in `filters.cs`. Run it and the output reads `Oh no, not found!`.

using System.Net;
try
{
    using var response = new HttpResponseMessage(
        HttpStatusCode.NotFound);
    response.EnsureSuccessStatusCode();
}
catch (HttpRequestException ex)
    when (ex.StatusCode == HttpStatusCode.NotFound)
{
    Console.WriteLine("Oh no, not found!");
}

Oh no, not found!

Flatten a collection of collections — Tip #001

Tue, 03 Nov 2026 05:00:00 GMT

SelectMany flattens nested sequences into one. Spread puts the result into a list.

SelectMany flattens nested sequences into one. Spread puts the result into a list. It is available since C# 12. The key line is `List<int> modern = [.. numbers.SelectMany(n => n)]` in `flatten.cs`. Run it and the output reads `1, 2, 3, 4, 5, 6, 7, 8, 9`.

int[][] numbers = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];

// classic LINQ
var values = numbers.SelectMany(n => n).ToList();

// C# 12: collection expression + spread
List<int> modern = [.. numbers.SelectMany(n => n)];

Console.WriteLine(string.Join(", ", modern));

1, 2, 3, 4, 5, 6, 7, 8, 9