C# 9 - Record Types Introduction & Deep-Dive

Record types are immutable reference types that provide value semantics for equality. Don't worry - record types aren't as complicated as they sound. Let's break it all down and see what record types are, how to implement them in C# 9, and why we should care about them.

Record types are introduced in C# 9 to allow developers to write immutable reference types. It means that the properties of an instance of a reference type cannot change after its initialization.

If we want to change the value of an existing object's property, we need to create a new instance. It is possible to inherit from a record type.

Record Types offer the following features:

- Immutability through read-only properties
- A constructor with properties as arguments
- Value-based equality checks
- A textual representation (ToString)
- A Deconstruct method

Record types are essentially a compiler feature. The developer writes a record type definition, and during compilation, the compiler generates a class based on a template.

Every situation where we could take advantage of one of the features record types provide is a potential use case for using record types instead of writing a class.

00:00 Introduction
00:33 Record Types Introduction
01:47 Cloning a record type
02:11 Record Types Inheritance
02:59 Value-based Equality
04:26 ToString Implementation
05:28 Record Types Internals - Generated Code (Advanced)
06:53 Record Types Features
08:12 Alternative Syntax
10:32 Alternative Syntax: Properties without init-setters
11:00 Alternative Syntax: Properties with default-setters
11:30 Alternative Syntax: Summary
12:05 Record Types: Add custom methods
12:33 Record Types: Use cases
13:49 Record Types: Conclusion

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CREDITS

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[ClaudioBernasconi]

What is your take on C# 9 Record Types? Will you use them? Why, or why not?

[parthlearning]

Thank you for sharing this great knowledge

[انامسلموكفى]

If the data does not change, we don't need to synchronise the access to it ?

[msnotif]

Hello. If I wanna to full clone a record. For example: var rec2=rec1 with { }; Is it the same as: var rec2=rec1; // is the 'with' necessary?

[ajeetmalviya]

Which tool are you using to convert into IL?

[Mortuus]

"var" is completely dead now (it has been before, too, because it is, by definition, less readable).
instead of...:
var person1 = new Person("John", "Adams");
write...:
Person person1 = new("John", "Adams");

it is dead now, since the alternative is more readable (Datatype, variable name, assignment) and shorter than the var syntax. From now on, don't use a language feature unless you need it - so for var it would be limited to very few cases such as ArrayLists or whatever.