c# - record types with collection properties & collections with value semantics

Question

In c# 9, we now (finally) have record types:

public record SomeRecord(int SomeInt, string SomeString);

This gives us goodies like value semantics:

var r1 = new SomeRecord(0, "zero");
var r2 = new SomeRecord(0, "zero");
Console.WriteLine(r1 == r2); // true - property based equality

While experimenting with this feature, I realized that defining a property of a (non-string) reference type may lead to counter-intuitive (albeit perfectly explainable if you think it through) behaviour:

public record SomeRecord(int SomeInt, string SomeString, int[] SomeArray);

var r1 = new SomeRecord(0, "test", new[] {1,2});
var r2 = new SomeRecord(0, "test", new[] {1,2});
Console.WriteLine(r1 == r2); // false, since int[] is a non-record reference type

Are there collection types with value semantics in .Net (or 3rd party) that may be used in this scenario? I looked at ImmutableArray and the likes, but these don't provide this feature either.

Answer 1

It looks like there is currently no such type available. It's not too difficult to roll your own though. As an example, see this gist which decorates an IImutableList and can be used as follows:

var r1 = new SomeRecord(0, "test", new[] { 1, 2 }.ToImmutableList().WithValueSemantics());
var r2 = new SomeRecord(0, "test", new[] { 1, 2 }.ToImmutableList().WithValueSemantics());
Console.WriteLine(r1 == r2); // true

Obviously beware of the performance implications for very large lists.