Record
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Definition
Built-in functionality for encapsulating immutable data.
C# 10 allows the record class syntax as a synonym to clarify a reference type, and record struct to define a value type.
Primary constructor
When you declare a primary constructor on a record, the compiler generates public properties for the primary constructor parameters.
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public record Person(string FirstName, string LastName);
// with the generated properties it is equivalent to
public record Person
{
public required string FirstName { get; init; }
public required string LastName { get; init; }
};
// record struct value type with immutable properties
public readonly record struct Point(double X, double Y);
// equivalent to
public record struct Point
{
public double X { get; init; }
public double Y { get; init; }
}
// record struct value type with mutable properties
public record struct Point(double X, double Y);
// equivalent to
public record struct Point
{
public double X { get; set; }
public double Y { get; set; }
}
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Immutability
Immutability means the data of the record don't change after its creation.
It is useful when you need thread-safe data-centric types or expect hash codes remaining the sames.
However, the data that a reference-type property refers to can be changed:
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public record Person(string Name, string[] PhoneNumbers);
Person person = new("Nicolas", new string[1] { "06-10-20-30-40" });
// the PhoneNumbers array is immutable, but the string in the array are mutable
person.PhoneNumbers[0] = "06-11-22-33-44";
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Value equality
Two record objects are equal if they are of the same type and store the same values.
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string[] phoneNumbers = [ "06-10-20-30-40" ];
Person person1 = new("Nicolas", phoneNumbers);
Person person2 = new("Nicolas", phoneNumbers);
Console.WriteLine(person1 == person2); // true
Person person1 = new("Nicolas", [ "06-10-20-30-40" ]);
Person person2 = new("Nicolas", [ "06-10-20-30-40" ]);
Console.WriteLine(person1 == person2); // false
public record Person(string Name, string[] PhoneNumbers);
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Nondestructive mutation
Allow to copy and modify the copy only.
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Person person1 = new("Nicolas", [ "06-10-20-30-40" ]);
Person person2 = person1 with { Name = "Audrey" };
var person3 = person1 with { }; // copy without modification
Console.WriteLine(person1 == person3); // true
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