C#•5mo ago

Optional parameters with dependency injection

Is it possible to have an optional parameter for a constructor with dependency injection. I know that dependency injection usually it implies it is a required dependency, but for example if the only dependency is an ILogger, then I don't really care if one was registered or not. EDIT: Changed ILogger<Test> to be nullable

public class Test
{
    private readonly ILogger<Test>? _logger;

    public Test(ILogger<Test>? logger = null) // does this work?
    {
        _logger = logger
    }

    public void DoSomething()
    {
        _logger?.LogInformation("Doing something...");
    }
}

public class Test
{
    private readonly ILogger<Test>? _logger;

    public Test(ILogger<Test>? logger = null) // does this work?
    {
        _logger = logger
    }

    public void DoSomething()
    {
        _logger?.LogInformation("Doing something...");
    }
}

5 Replies

Angius•5mo ago

You're injecting an ILogger<T> not ILogger<T>? so it cannot be null I mean, theoretically it can, if you want to write bad code But it shouldn't Also, unless you're doing some conditional registration (why?) then it will either be registered, or not, and you will know which it is So IMHO it doesn't make much sense to make it nullable

nathanAjacobs•5mo ago

Those are all fair, but what if this code is in a library, and it might not necessarily be used by dependency injection. So having it as an optional parameter might suit the situation where it is just being newed up manually

Angius•5mo ago

I guess

nathanAjacobs•5mo ago

So if it exists in a library, I don't know if the consumer actually has an ILogger registered

not guilty•5mo ago

i would say optional parameters means passing putting it into a class in a nullable field but it depends on what it is

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Optional parameters with dependency injection