Data Classes

LoginResource.cs

using System;
using System.Collections.Generic;

/*
 * public data class LoginResource
 * {
 *     public string Username { get; }
 *     public string Password { get; } 
 *     public bool RememberMe { get; } = true;
 * }
 */
public sealed class LoginResource : IEquatable<LoginResource> {
    public struct Builder
    {
        public string Username;
        public string Password;
        public bool RememberMe;
    }
    
    public static void Init(ref Builder builder)
    {
        builder.RememberMe = true;
    }
    
    private readonly Builder _builder;
    
    public LoginResource(Builder builder) => _builder = builder;
    
    public string Username => _builder.Username;
    public string Password => _builder.Password;
    public bool RememberMe => _builder.RememberMe;
    
    public override bool Equals(object obj)
    {
        return Equals(obj as LoginResource);
    }
    
    public bool Equals(LoginResource that)
    {
        if (that is null) return false;
        
        var eq1 = EqualityComparer<string>.Default;
        return eq1.Equals(Username, that.Username)
            && eq1.Equals(this.Password, that.Password)
            && this.RememberMe == that.RememberMe;
    }

    public override int GetHashCode()
    {
        var eq1 = EqualityComparer<string>.Default;
        var hashCode = -736459255;
        hashCode = hashCode * -1521134295 + eq1.GetHashCode(Username);
        hashCode = hashCode * -1521134295 + eq1.GetHashCode(Password);
        hashCode = hashCode * -1521134295 + RememberMe.GetHashCode();
        return hashCode;
    }

    public override string ToString()
    {
        return $"{{{nameof(Username)} = {Username}, {nameof(Password)} = {Password}, {nameof(RememberMe)} = {RememberMe}}}";
    }
    
    public static bool operator ==(LoginResource x, LoginResource y) {
        return x is LoginResource @this && @this.Equals(x);
    }
    
    public static bool operator !=(LoginResource x, LoginResource y) {
        return !(x == y);
    }
}

Won't this copy the builder on the stack for the constructor call? Can you add an example?

    public static bool operator ==(LoginResource x, LoginResource y) {
        return x is LoginResource @this && @this.Equals(x); // <- also probably should be: @this.Equals(y)
    }

Isn't that going to return false for both-null case?

public static void ValidateEqualsOperator()
{
    LoginResource x = null, y = null;
    Assert.True(x == y); // throws
}