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.

You can implement this yourself, but beware of the implications if you need this in a production-ready way. It's not so simple as it may seem at first sight, as this answer by @ryanholden8 demonstrates!

For my use case (and as a simplified example) I went along with 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.