ℹ️ This article was originally published in Portuguese on Medium. You can read the original version here.

Who has never lost good minutes searching the internet when they had to override the GetHashCode method? I have!

It was quite common to find confusing implementations like this one:

public class Person
{
    public int Id { get; set; }

    public string Name { get; set; }

    public override bool Equals(object obj) => // ...

    public override int GetHashCode()
    {
        int hash = 13;

        hash = (hash * 7) + Id.GetHashCode();
        hash = (hash * 7) + Name.GetHashCode();

        return hash;
    }
}

Really, it wasn’t an easy task to choose an implementation that would generate a good hash. That’s right, it wasn’t! Since .NET Core version 2.1, a new struct called System.HashCode has been added, which makes implementing the method much — much — easier.

The Person class, presented earlier, can now be implemented like this:

using System;

public class Person
{
    public int Id { get; set; }

    public string Name { get; set; }

    public override bool Equals(object obj) => // ...

    public override int GetHashCode() => HashCode.Combine(Id, Name);
}

Much easier, right!?

The static Combine method from the example can generate hashes by combining up to eight parameters. This is the simplest way to use the new API. However, it also provides instance methods that can be used to generate your hashes, such as ToHashCode. You can check more examples in the official documentation of the struct.

The proposal for this API started being discussed in this issue on the CoreFx GitHub, in December 2016, and was released with .NET Core version 2.1 on May 30, 2018. It’s also available through the NuGet package Microsoft.Bcl.HashCode for earlier Framework versions, but it’s still in preview.

So what do you think of this new feature? I really liked it! It’s always good when we reduce the complexity of routine implementations and can focus on what really matters: our system’s business rules.

References #

• Proposal: Add System.HashCode to make it easier to generate good hash codes
• Easier GetHashCode implementation in .NET Core 2.1
• System.HashCode