Today, I'm going to share some fascinating things you can do with records and anonymous types. I will introduce you to the concept of non-destructive mutation. And I will talk about when and why we might want to use this C# language feature.
With C# 9 we can use records that are a new reference type. C# 10 introduced record structs so that you can define records as value types. Records are distinct from classes in that record types use value-based equality.
Let's see how we would define a
public record Food(string Name, double Price);
This way of declaring a
record is called a positional record.
The constructor we have defined here is called the primary constructor.
Price properties are init only properties.
This means they can only be set in the constructor or using a property initializer.
Since our properties are init only, is there any way to change their value?
We said we can't modify the properties of our
record, because the properties are init only.
However, we can use the
with expression (introduced in C# 9) to create a new instance
of our record with modified values.
Let's see how we would use the
var banana = new Food("🍌", 1.95);
var bananaOnSale = banana with
Price = 0.99
It's important to highlight two things here:
- The original banana instance remains unchanged
withexpression creates a new record instance with only the
I mentioned Anonymous Types in the title, so let me show you something interesting you can do with them.
Did you know that you can use the
with expression with anonymous types?
Just a reminder that the
with expression is available from C# 9 and later.
Let's create an anonymous type:
var apple = new
Name = "🍎",
Price = 1.21
This is how we can modify it using the with expression:
var orange = apple with
Name = "🍊"
And again the same rules apply:
- The original apple instance remains unchanged
- The with expression creates a new anonymous type instance with only the Name property modified
I found this feature useful in LINQ method chains.
For example, loading an anonymous type from the database where some properties have a default value. You can then use this feature to calculate the values for these properties in memory.