One of the talks on day 2 of SDD 2023, was called "Let's stop programming like 2017". The talk was held by Richard Blewitt (@RichardBlewitt) and Andrew Clymer (@AndrewClymer) from https://www.rocksolidknowledge.com/. I've been to a few talks with them and they are an absolute blast. Always lots of good laughs - just the way I like it!

In the talk they went through some of the improvements that has been made over the last years in C#. I will not go through all of them, but one really stood out to me: Pattern matching

In the bustling world of code, finding specific properties can be as challenging as spotting Waldo in a crowded scene. But fear not! C# 11's property pattern matching saves the day! It's a stylish and powerful feature that lets you uncover the hidden treasures of your objects with ease. So get out your magnifying glass and get ready to unravel the secrets of this exciting feature, transforming the search for Waldo (or any property) into a stylish and enjoyable code adventure.

Property pattern matching

One of the types of pattern matching that we can do is called property pattern matching. Property pattern matching in C# 11 is a feature that allows you to match against specific properties within objects. It provides a concise and expressive syntax for performing pattern matching based on the values of object properties.

With property pattern matching, you can easily extract relevant information or perform specific actions based on the properties of an object. It simplifies complex conditional logic by enabling you to match against property values directly within patterns.

The syntax for property pattern matching involves specifying the property name and its expected value in a pattern. This feature is particularly useful when dealing with objects that have multiple properties and you need to selectively handle different combinations of property values. It enhances code readability and conciseness, making it easier to write and understand complex matching scenarios.

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public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
}

public string GetGreeting(Person person)
{
    return person switch
    {
        { Name: "Alice" } => "Hello, Alice!",
        { Name: "Bob", Age: 25 } => "Hey Bob, you're 25!",
        { Age: >= 18 } => "Welcome, adult!",
        _ => "Greetings!"
    };
}

In the example above, we have a `Person` class with properties `Name` and `Age`. The `GetGreeting` method takes a `Person` object and returns a greeting based on different matching patterns.

In the first pattern, `{ Name: "Alice" }`, we match against a `Person` object with the name "Alice". If the `Name` property matches "Alice", the corresponding greeting "Hello, Alice!" is returned.

In the second pattern, `{ Name: "Bob", Age: 25 }`, we match against a `Person` object with the name "Bob" and age 25. If both properties match the specified values, the greeting "Hey Bob, you're 25!" is returned.

The third pattern, `{ Age: >= 18 }`, matches any `Person` object where the `Age` property is greater than or equal to 18. If the age condition is met, the greeting "Welcome, adult!" is returned.

Finally, the underscore `_` acts as a catch-all pattern that matches any `Person` object not matched by the previous patterns. In this case, the generic greeting "Greetings!" is returned.

Property pattern matching allows for concise and expressive code by directly matching against object properties within patterns, making it easier to handle complex conditional logic and extract values from objects.

Type pattern matching

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public string GetShapeInfo(object shape)
{
    return shape switch
    {
        Circle c => $"Circle with radius {c.Radius}",
        Rectangle r => $"Rectangle with width {r.Width} and height {r.Height}",
        _ => "Unknown shape"
    };
}

public class Circle
{
    public double Radius { get; set; }
}

public class Rectangle
{
    public double Width { get; set; }
    public double Height { get; set; }
}

In the example above, we have a GetShapeInfo method that takes an object representing a shape. We use type pattern matching within the switch statement to determine the type of the shape and provide specific information based on that type.

When the shape matches the Circle type, we can access its properties directly within the pattern and return a formatted string with the radius value.

Similarly, when the shape matches the Rectangle type, we can access its properties and return a formatted string with the width and height values.

The underscore _ acts as the default pattern and matches any object that doesn't match the previous patterns. In this case, it returns "Unknown shape".

Type pattern matching allows us to check and extract specific types from objects, making it easier to handle different cases and provide type-specific behavior or information.