In this article, we are going to cover a new addition to C# 10, known as extended property patterns. Pattern matching appears to be one of the priorities in the development of C# as a language in the last several years.
Every new release adds a few improvements to this paradigm, so let’s have a look at what’s new in this version.
What Is Pattern Matching?
Pattern matching is a paradigm for evaluating expressions to check whether they meet certain criteria. In other words, it is an evolution of the good old if-else instructions, which, in some cases, allows for a more concise and clear code.
Pattern matching is ubiquitous in functional languages, such as F#, whereas C# started supporting it since version 7.
Property Patterns Matching
Property patterns added in C# 8.0 allow matching based on the properties of the object.
Let’s see how we can use them in a switch expression to evaluate a set of conditions.
First, we are going to declare a simplified data model, but with enough properties to show the sweetness of the new syntactic sugar:
record Order(Payment Payment, Customer Customer); record Payment(Price Price, DateTime? PaymentDate = null); record Price(string Currency, decimal Amount); record Customer(string Name, string Group);
Now, we use this Order to create an instance of an OrderProcessor class in a variation of a factory pattern:
public static string GetPreCSharp10Syntax(Order order) => order switch
{
{ Payment: { Price: { Currency: "BTC" } } } => "CryptoOrderProcessor",
{ Customer: { Group: "Banking" }, Payment: { Price: { Currency: "JPY" } } } => "JapaneseBankingProcessor",
{ Payment: { Price: { Amount: > 5000000} } } or { Customer: { Group: "VIP" } } => "ImportantOrderProcessor",
_ => "DefaultOrderProcessor"
};
The example shows the switch expression combined with property pattern matching.
The usage of pattern matching and expression-bodied members makes the syntax very succinct and reduces the overall size of the method. Although the syntax isn’t terrible, the way of accessing the nested properties feels a bit unnatural.
Extended Property Patterns Matching
The extended property patterns build on top of the existing feature. They allow a more concise and readable syntax, by offering the well-known dot-notation for accessing properties of objects, rather than requiring usage of curly braces.
Let’s see the same example rewritten with the new approach:
static class OrderProcessorFactory
{
public static string Get(Order order) => order switch
{
{ Payment.Price.Currency: "BTC" } => "CryptoOrderProcessor",
{ Customer.Group: "Banking", Payment.Price.Currency: "JPY" } => "JapaneseBankingProcessor",
{ Payment.Price.Amount: >= 500000 } or { Customer.Group: "VIP" } => "ImportantOrderProcessor",
_ => "DefaultOrderProcessor"
};
}
Clearly, this improvement is not a revolution, but a very welcome evolution.
Conclusion
In this article, we had a glance at the property pattern matching improvement added in C# 10. While it’s not a ground-breaking change, it surely allows a more “natural” and fluent syntax, which will positively affect the pattern matching adoption in C#.