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C# 9.0 Perks

yurieastwood profile image Yuri Eastwood ・2 min read

Hello everyone!

C# 9.0 is the new kid on the block for language enthusiasts.

There are quite a few new "goodies" in it, here I'll talk a little bit about some that caught my attention, be it because it's something that will make my everyday easier or something that community has talked a lot about it and it's finally here!

I'll cover Init-only properties and accessors, target-typed new expressions and records & with-expressions.

Got all of those objects that should be set only in initialization? Problem solved!
The init accessor was just introduced to make your day easier.

Public class Product
{
    public string? Name { get; init; }
    public string? Brand { get; init; }
}
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With the aforementioned declaration any subsequent assignment to those properties will throw a compile time error!
This means that initialization onwards the state of the object is totally protected from mutation.

var product = new Product { Name = "Tomato", Brand = "XYZ" }; // YAY!
product.Brand = "GEEZ"; // NOPZ!
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And with target-type new expressions we can kiss goodbye to verbose declarations!

Product product = new { Name = "Tomato", Brand = "XYZ" };
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Which would be especially nicer if we were dealing with arrays or lists!

Product[] products = { 
    new { Name = "Tomato", Brand = "XYZ" }, 
    new { Name = "Potato", Brand = "XYZ" }, 
    new { Name = "Tomato", Brand = "GEEZ" }, 
    new { Name = "Potato", Brand = "GEEZ" }
};
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We do have a trade-off between var and target-type new expressions, but the freedom to decide what's better in each situation is what thrills me.

Continuing on our previous subject: want the whole object to be immutable, just like a value type behavior? Combine it with Record class!

Public record Product
{
    public string? Name { get; init; }
    public string? Brand { get; init; }
}
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In these cases we normally represent new states by creating a whole new object based on the values of existing ones. And this is where With-expressions come into place!

We can create the new object by only stating what's different:

Product product = new { Name = "Tomato", Brand = "XYZ" };
var otherProduct = product with { Brand = "GEEZ" };
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There are many other features that might help you out such as static anonymous functions, covariant returns and improved pattern matching. To learn more take a look in the "What's new in C# 9.0" documentation.

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