slides.md

marp	author	theme	class
true	Rasmus Lystrøm	default	invert

Survey during the academic quarter

https://www.menti.com/ code: 5942 1139

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Questions

• How to setup tests?
• Testing private methods?
• How to use fluent assertions?

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C♯ 03: Lambdas and LINQ

Rasmus Lystrøm Associate Professor ITU

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Topics

Delegates Anonymous methods Lambda expressions Local functions Anonymous types Tuples Records Extension methods LINQ

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Delegates

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Delegates – Building block for Higher-order functions

public delegate int BinaryOperation(int x, int y);

var add = new BinaryOperation(
    delegate (int x, int y)
    {
        return x + y;
    }
);

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Delegates

Demo

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Lambda Expressions

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Lambda Expressions

Action<string> write = s => Console.WriteLine(s);

Func<int, int> square = a => a * a;

Predicate<City> b = c => c.Name.StartsWith("B");

Converter<double, double> ftoC = c => c * 9.0 / 5.0 + 32.0;

...

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Local Functions

static void Main(string[] args)
{
    int square(int a) { return a * a; };

    Console.WriteLine(square(16));
}

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Local Functions

Demo

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Prerequisites

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Anonymous types

var question = new
{
    Title = "The answer...?",
    Answer = 42
};

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(Tuples)

var s = Tuple.Create("Clark Kent", "Superman");

var b = ("Bruce Wayne", "Batman");

var f = (name: "Barry Allen", alterEgo: "The Flash");

var random = new Random();

IEnumerable<(float x, float y)> GenerateCoordinates()
{
    yield return (random.NextSingle() * 100, random.NextSingle() * 100);
}

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Records

public record Superhero(string Name, string AlterEgo, DateTime FirstAppearance);

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Data: Collection Initializer

IEnumerable<City> cities = new[]
{
    new City(1, "Berlin"),
    new City(2, "Hamburg"),
    new City(3, "Frankfurt")
};

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Data: Collection + Object Initializer

IEnumerable<City> cities = new[]
{
    new City { Id = 1, Name = "Berlin" },
    new City { Id = 2, Name = "Hamburg" },
    new City { Id = 3, Name = "Frankfurt" }
};

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Extension Methods

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Built-in Extension methods

var count = cities.Count();

var sort = cities.OrderBy(c => c.Name);

var filter = cities.Where(c => c.Name.Contains("i"));

var pick = cities.FirstOrDefault(c => c.Id == 2);

var all = cities.All(c => c.Name.Length < 10);

var any = cities.Any(c => c.Name.StartsWith("B"));

var project = cities.Select(c => c.Name);

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Create your own extension method

public static class Extensions
{
    public static int WordCount(this string str) =>
        str.Split(new[] { ' ', '.', '?' },
                  StringSplitOptions.RemoveEmptyEntries)
           .Length;
}

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Extension methods

Demo

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LINQ - Language INtegrated Query

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LINQ

var sorted = from c in cities
             where c.Name.Contains("i")
             orderby c.Name descending
             select new { Name = c.Name };

Extension Methods Version

var sorted = cities.Where(c => c.Name.Contains("i"))
                   .OrderByDescending(c => c.Name)
                   .Select(c => new { Name = c.Name });

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LINQ

Demo

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Thank you