C#•2y ago

✅ public readonly bool Equals(...)? - SOLVED

I created struct for my needs of representing a phone number prefix and intellisense offered me a "potential fix" which after applying added readonly modifier to a method return type? Can you explain to me what this does as I see it first time in my 5 years of c#-ing?

public struct PhoneNumberPrefix : IEqualityComparer<PhoneNumberPrefix>
{   
    public PhoneNumberPrefix(int intValue, string stringValue)
    {
        IntValue = intValue;
        StringValue = stringValue;
    }
    public int IntValue { get; set; } = 0;
    public string StringValue { get; set; } = "";

    public readonly bool Equals(PhoneNumberPrefix x, PhoneNumberPrefix y)
    {
        return x.IntValue == y.IntValue && x.StringValue == y.StringValue;
    }

    public  int GetHashCode(PhoneNumberPrefix obj)
    {
        throw new NotImplementedException();
    }
}

public struct PhoneNumberPrefix : IEqualityComparer<PhoneNumberPrefix>
{   
    public PhoneNumberPrefix(int intValue, string stringValue)
    {
        IntValue = intValue;
        StringValue = stringValue;
    }
    public int IntValue { get; set; } = 0;
    public string StringValue { get; set; } = "";

    public readonly bool Equals(PhoneNumberPrefix x, PhoneNumberPrefix y)
    {
        return x.IntValue == y.IntValue && x.StringValue == y.StringValue;
    }

    public  int GetHashCode(PhoneNumberPrefix obj)
    {
        throw new NotImplementedException();
    }
}

And yes... It compiles 😄

6 Replies

artya•2y ago

So the readonly modifier means that the

Equals

Equals

method is restricted from modifying any data in your struct

Honza K.OP•2y ago

nvm, I just found the documentation for it 😄 https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/proposals/csharp-8.0/readonly-instance-members I wonder if it offers any performance benefits?

Readonly instance members - C# 8.0 draft feature specifications

This feature specification describes the syntax for declaring and using readonly instance members.

artya•2y ago

I highly doubt there are performance benefits The method itself is simple enough to where even if you did gain performance benefits they'd most likely not be noticable

Honza K.OP•2y ago

reading through the link I posted... it can save you some copies of the structs when using in parameters... so in case of equals method it wont do much, but in case of a bigger structures it can save memory

artya•2y ago

👍 you asked the question and I learned something new today

Honza K.OP•2y ago

haha, same here, thank you 😄

Gaming

Programming

✅ public readonly bool Equals(...)? - SOLVED