C#•10mo ago

❔ Custom Copy Semantics for `record struct`?

Hey all - I'm having a hard time figuring out how to (and if it's even supportedt) to do custom copy semantics for record structs. Changing my record type to a record/record class properly calls the copy ctor, but if it's a record struct, when I use with the copy ctor isn't being called. Would love any help here

8 Replies

Thinker•10mo ago

If you have a record struct r, with just does

R r2 = r1;
r2.SomeProperty = someValue;

R r2 = r1;
r2.SomeProperty = someValue;

So it doesn't call a constructor or method, it just copies the entire struct memory on the stack.

bacon•10mo ago

so this doesn't apply to record structs? https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/with-expression#custom-copy-semantics

with expression - create new objects that are modified copies of ex...

Learn about a with expression that performs nondestructive mutation of C# records and structures. The with keyword provides the means to modify one or more properties in the new object.

MODiX•10mo ago

Thinker

sharplab.io (click here)

var person = new Person("John Doe", 40);
var person2 = person with { Age = 41 };
record struct Person(string Name, int Age) {
    public Person(Person other) : this(other.Name, other.A... {
        Console.WriteLine("copy");
    }
}

var person = new Person("John Doe", 40);
var person2 = person with { Age = 41 };
record struct Person(string Name, int Age) {
    public Person(Person other) : this(other.Name, other.A... {
        Console.WriteLine("copy");
    }
}

React with ❌ to remove this embed.

Thinker•10mo ago

Not according to Sharplab at least

Person person = new Person("John Doe", 40);
Person person2 = person;
person2.Age = 41;
Person person3 = person2;

Person person = new Person("John Doe", 40);
Person person2 = person;
person2.Age = 41;
Person person3 = person2;

bacon•10mo ago

this feels like an annoying oversight lol

Thinker•10mo ago

Ask in #roslyn if you feel like it

bacon•10mo ago

thanks for the confirmation and help though @🌈 Thinker 🌈

Accord•10mo ago

Looks like nothing has happened here. I will mark this as stale and this post will be archived until there is new activity.

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❔ Custom Copy Semantics for `record struct`?