Records simplify dependency injection for MediatR handlers

MediatR command handlers when used with dependency injection often feel... boilerplatey.

Let's look at an example handler with two injected services.

public sealed class SendEmailCommandHandler
    : IRequestHandler<int, int>
{
    private readonly IEmailSender _emailSender;
    private readonly IUserRepository _userRepository;
    private readonly ILogger _logger;

    public SendEmailCommandHandler(
        IEmailSender emailSender,
        IUserRepository userRepository,
        ILogger logger
    )
    {
        _emailSender = emailSender;
        _userRepository = userRepository;
        _logger = logger;
    }

    // ...rest of the handler goes below
}

As seen on the above example, creating a constructor, fields and assigning them is a bit repetitive. Even with modern tooling, it still feels as...not really necessary.

Enter records. With its feature of primary constructors, the above code can be simplified to:

public sealed record SendEmailCommandHandler(
        IEmailSender _emailSender,
        IUserRepository _userRepository,
        ILogger _logger
    ) : IRequestHandler<int, int>
{
    // ...rest of the handler goes below
}

If you squint, it almost looks like a public method definition. Quite a nice improvement: shorter file and easier on the eyes.