public static class TestRecordTypes
{
public static void RunTest()
{
List<Person> people = new List<Person>()
{
new Person("John", "Doe", "home"),
new Person("John", "Doe", "Away"),
new Person("Billy", "Doe", "home"),
new Person("Billy", "Doe", "home"),
new Person("Batty", "Bo", "home"),
};
var peopleHash = people.ToHashSet();
Debug.WriteLine($"{peopleHash}");
}
}
public record Person(string FirstName, string LastName)
{
string _location;
public Person(string firstName, string lastName, string location):
this(firstName, lastName)
{
_location = location;
}
}
With this test I had hoped that peopleHash list would only have 3 records, but I get 4 as the equality appears to be including the non init parameter location.
Is there a way to get the list of 3 records I want where the comparison is performed on the init properties only and ignores the additional location parameter?
Answer
You want to change the IEquatable<Person> implementation. For that, you can add Equal and override GetHashCode in the record:
public record Person(string FirstName, string LastName)
{
string _location;
public Person(string firstName, string lastName, string location) :
this(firstName, lastName) => _location = location;
public virtual bool Equals(Person other)
{
if (ReferenceEquals(null, other)) return false;
if (ReferenceEquals(this, other)) return true;
return FirstName == other.FirstName && LastName == other.LastName;
}
public override int GetHashCode() => HashCode.Combine(FirstName, LastName);
}
then the test passes:
[TestMethod]
public void HashTest()
{
List<Person> people = new List<Person>()
{
new ("John", "Doe", "home"),
new ("John", "Doe", "Away"),
new ("Billy", "Doe", "home"),
new ("Billy", "Doe", "home"),
new ("Batty", "Bo", "home"),
};
var peopleHash = people.ToHashSet();
Assert.AreEqual(3, peopleHash.Count);
}