How to initialise a Class using the C#12 Primary Constructor

Question

How do you initialise a class using the C#12 primary construtor syntax. I know how to do it using dependency injection but cant find any docs showing how to do it with a normal class.

here is what I want to change to the primary constructor syntax.

internal class AutoHttpClient : IAutoHttpClient
{
    private readonly HttpClient httpClient;

    public AutoHttpClient()
    {
        httpClient = new HttpClient();
    }

}

im guessing that just doing the below will not work or will it?

internal class AutoHttpClient(HttpClient httpClient) : IAutoHttpClient
{
}

I have also looked onlint but all the examples aside of DI were using base types like int etc. Thanks for the help.

Answer 1

Your second example works just fine:

internal class AutoHttpClient(HttpClient httpClient)
{
    public async Task SendRequestAsync()
    {
        await httpClient.GetAsync("url");
    }
}

Note that in this case httpClient is basically a closed-over variable, and not a named private readonly field. If you want to prevent the internal code from changing the value of httpClient after construction, you'll need to declare a separate field. But you can still initialize it from the primary constructor's parameter.

internal class AutoHttpClient(HttpClient httpClient)
{
    private readonly HttpClient httpClient = httpClient;
    public async Task SendRequestAsync()
    {
        await httpClient.GetAsync("url");
    }
}

In this case, the field overrides the variable name httpClient, so the compiler doesn't make the closure field available in your methods: only in the field initializers. So when the method references httpClient it's referencing the declared field instead.