Choosing a type

The kind of type follows from what the thing is.

• A class has identity, changing state or inheritance, such as a customer or a service. EF Core entities belong here: its guidance is to avoid records for them, because it tracks entities by reference equality.
• A record is its data, so two with the same values are the same thing, such as an address or a DTO. It has value equality, with and ToString. The positional or property form is a separate choice (see the () and noteRecords: the () way and the {} wayA record can be declared with its data in parentheses or in a body.Opens in a new tab).
• A struct is a small, immutable single value, preferably readonly. A readonly record struct adds value equality and with.
• An interface is a contract that unrelated types can fulfil. An abstract class adds shared behavior (see interfaces versus abstract classesInterfaces versus abstract classesTwo ways to define what a type must offer, and when each one fits.Opens in a new tab).

	Kind	Copying	Equality by default	Inheritance
class	Reference	Shares the object	Reference	One base class, plus interfaces
struct	Value	Copies the value	Compares fields	Interfaces only
interface	Contract	Not applicable	Not applicable	Implemented by many types
record	Reference	Shares, and with makes a copy	By value	One base record, plus interfaces
record struct	Value	Copies the value	By value	Interfaces only

A wrong choice shows up later as a copy that wasn’t independent, an equality check that returns false, or an allocation on a hot path (see value types and reference typesValue types and reference typesA value type variable holds the value. A reference type variable holds a reference to an object.Opens in a new tab).