Round #889

Write a custom equality comparer (IEqualityComparer<Person>) that treats two Person records as equal when Email lowercased matches. Include GetHashCode.

```csharp using System; using System.Collections.Generic; public record Person(string Email, string Name); public class PersonEqualityComparer : IEqualityComparer<Person> { public bool Equals(Person? x, Person? y) { if (x == null && y == null) return true; if (x == null || y == null) return false; return string.Equals(x.Email.ToLower(), y.Email.ToLower(), StringComparison.Ordinal); } public int GetHashCode(Person obj) { return obj.Email.ToLower().GetHashCode(); } } class Program { static void Main() { var person1 = new Person("John.Doe@example.com", "John Doe"); var person2 = new Person("john.doe@example.com", "Jane Doe"); var comparer = new PersonEqualityComparer(); Console.WriteLine(comparer.Equals(person1, person2)); // Outputs: True } } ``` In this code: - We define a `Person` record with `Email` and `Name` properties. - We create a custom `PersonEqualityComparer` class that implements `IEqualityComparer<Person>`. - The `Equals` method checks if the lowercased `Email` properties of two `Person` objects are equal. - The `GetHashCode` method returns a hash code for a `Person` object based on the lowercased `Email` property. - In the `Main` method, we demonstrate the usage of the custom comparer by comparing two `Person` objects with different email cases.

```csharp public class PersonEmailEqualityComparer : IEqualityComparer<Person> { public bool Equals(Person? x, Person? y) { if (x == null && y == null) return true; if (x == null || y == null) return false; return string.Equals(x.Email, y.Email, StringComparison.OrdinalIgnoreCase); } public int GetHashCode(Person obj) { return obj.Email.ToLowerInvariant().GetHashCode(); } } ``` This comparer uses `StringComparison.OrdinalIgnoreCase` for case-insensitive comparison in the `Equals` method and `ToLowerInvariant` in the `GetHashCode` method to ensure consistent hash codes for the same email address regardless of case.