Deep equality for C# types

Description

In F# code we often have to use data types that are defined in C#. These types usually don’t have equality defined, and therefore only get referential equality.

It would be useful if FsUnit would provide a mechanism to still be able to structurally compare these types, similarly to how FluentAssertions does in its BeEquivalentTo method for C#:

actual.Should().BeEquivalentTo(expected, "reason")

Repro steps

1. Have a C# defined class like:

public sealed class Persion { 
  public string Name { get; set; }
  public int Age { get; set; }
}

1. Wrap it in F# union:

type User = User of Person

// Notice that the person inside is "the same"
let userA = User (Person(Name = "a", Age = 1))
let userB = User (Person(Name = "a", Age = 1))

1. Compare these two values:

// this says "no"
userA |> should equal userB

Expected behavior

I suggest that it’d be possible to have an operation that would allow the previous example to pass. It can be named beEquivalentTo or somehow else.

The operation can detect F# types (or presence for equivalence) and do what equal does, otherwise it can do what FluentAssertions does currently (takes a set op public fields and properties and runs comparison on them).

Actual behavior

The given example fails the test

Known workarounds

I can’t come up with a workaround that can work for an arbitrarily nested case.

[sergey-tihon]

FsUnit is an assertion library that supports DSL on top of popular unit testing frameworks. I think that equality should be provided by the type (e.g. Person).

Option1: If you need equality for C# types (and cannot define them in F# ☺️) you may search for C# source generator library that will generate proper equality for your types.

Option2: Reference library like DeepEqual and tiny F# layer on top for assertions

[CaptnCodr]

@AlexeyRaga I’ll close this here. This is out of our scope.