How to make Record case insensitive.

[TruePluto]

I have some code such as following

Person person1 = new(FirstName: "Nancy", LastName: "davolio"); //lowercase
Person person2 = new(FirstName: "Nancy", LastName: "Davolio");
Person person3 = new(FirstName: "Nancy", LastName: "Davolio");
Console.WriteLine(value: person1 == person2); // output:expect True but actually False ----
Console.WriteLine(value: person3 == person2); // output: True
Console.WriteLine(value: ReferenceEquals(objA: person1, objB: person2)); // output: False
Console.WriteLine(value: ReferenceEquals(objA: person3, objB: person2)); // output: False
Console.WriteLine(value: "Hello, World!");

public record Person(string FirstName, string LastName);

Output is

False ----here-----
True
False
False
Hello, World!

Meaning Record is case sensitive， but I want to make it case insensitive. what am I missing?
Thanks for your attention.

[CyrusNajmabadi]

Override .Equals in your record to implement whatever equality semantics you want.

[CyrusNajmabadi]

@TruePluto: public override bool Equals(Person p) { ... }. Put whatever logic you want in that to compare your instance to 'p'.

[TruePluto]

I made a console app following your advice

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net6.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

</Project>

and C#

Person p1 = new Person("HELLO", "KITTY");
Person p2 = new Person("hello", "kitty");
Console.WriteLine(p1==p2);  


public record Person(string FirstName, string LastName)
{
    public override bool Equals(Person? p)
    {
        if(p == null) return false; 
        if(p == this) return true;
        return
            string.Equals(FirstName, p.FirstName, StringComparison.InvariantCultureIgnoreCase) &&
            string.Equals(LastName, p.LastName, StringComparison.InvariantCultureIgnoreCase)
            ;
    }
}

I got a compile error
"CS0115 Person.Equals(Person?)" no suitable method found to override

Thank you for your attention

[yaakov-h]

https://sharplab.io/#v2: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

[DavidArno]

@yaakov-h, warning CS8851: 'Person' defines 'Equals' but not 'GetHashCode' is significant here. GetHashCode needs to be redefined to handle the case-insensitivity.

[yaakov-h]

only if you make use of the hashcode - fortunately there's a nice compiler warning there as a reminder

[TruePluto]

I want to use the class person as key for a dictionary class such as

public class Portfolio{...}
public record Person (string FirstName, string LastName);
public class PersonProfolioDict : Dictionary<Person, Portfolio> {...};

So I believe the function GetHashCode() is necessary. I wrote the code as following

public record Person(string FirstName, string LastName)
{
    public virtual bool Equals(Person? p)
    {
        if (ReferenceEquals(p, null)) return false;
        if (ReferenceEquals(p, this)) return true;
        return
            string.Equals(FirstName, p.FirstName, StringComparison.InvariantCultureIgnoreCase) &&
            string.Equals(LastName, p.LastName, StringComparison.InvariantCultureIgnoreCase)
            ;
    }
    public override int GetHashCode()
    {
        return HashCode.Combine(FirstName.ToUpperInvariant(), LastName.ToUpperInvariant());
        //for Net <6.0
        //return FirstName.ToUpperInvariant( ).GetHashCode() ^ LastName.ToUpperInvariant().GetHashCode();
    }
}

Is it correct?
I don't know whether it is a good idea to give attributes to indicate the string compare mode
such as

public record Person
    (
        [StringComparison(StringComparison.InvariantCultureIgnoreCase)]
        string FirstName,
        [StringComparison(StringComparison.InvariantCultureIgnoreCase)]
        string LastName
    );

Thank you all for your attention!

[yaakov-h]

StringComparer.InvariantCultureIgnoreCase.GetHashCode(...) should avoid a string allocation and therefore be a little bit faster.

[CyrusNajmabadi]

I don't know whether it is a good idea to give attributes to indicate the string compare mode such as

It's a fine idea. We leave it to Roslyn or the community to make a determination if someone wants to write a generator that would key off such things like that and generate appropriate Equals/GetHashCode overrides. It's explicitly been chosen to be external to the language. :)

Thanks!

[iam3yal]

Another alternative is to do something like this:

public sealed record Person(Name FirstName, Name LastName);

public readonly struct Name : IEquatable<Name>
{
    public readonly string _value;

    public Name(string value)
       => _value = value;

    public bool Equals(Name other)
    {
        return string.Equals(
            _value, 
            other._value, 
            StringComparison.InvariantCultureIgnoreCase);
    }

    public override int GetHashCode()
        => StringComparer.InvariantCultureIgnoreCase.GetHashCode(_value);

    public static implicit operator string(Name name) => name._value;
    public static implicit operator Name(string value) => new Name(value);
}