Proposal: allow typeof(this) to reference the current class

[LWChris]

For initialization of a log4net logger, you have two suboptimal options:

Option 1

private static readonly ILog _log = LogManager.GetLogger(typeof(MyClass));

This works well, but you need to remember to adjust MyClass every time you copy that line (which happens a lot).

Option 2

private static readonly ILog _log = LogManager.GetLogger(System.Reflection.MethodBase.GetCurrentMethod()?.DeclaringType);

This can be copy pasted, but it's quite convoluted and it uses reflection to do what could be known at compile time.

---

Allowing to write

private static readonly ILog _log = LogManager.GetLogger(typeof(this));

would mean the compiler would use the innermost class that the code is currently wrapped in. I know that this doesn't make sense in a static context, but allowing that keyword to appear within a typeof() expression, reading as "type of this" should be clear enough. It's basically the rough equivalent of VB.NET's MyClass keyword.

[CyrusNajmabadi]

Wouldn't typeof(class) make more sense?

[colejohnson66]

And what if it's a struct or record? typeof(struct) and typeof(record) would be fine with me, but typeof(this), while a bit illogical, is a singular form. Not to mention what a record struct would be - typeof(record struct)?

[333fred]

it uses reflection to do what could be known at compile time.

My problem with this proposal is that the behavior I actually expect requires reflection, or a hidden type parameter. I expect this sample to print Derived:

var d = new Derived();
d.M();

public class Base
{
    public void M() => Console.WriteLine(typeof(this).Name);
}

public class Derived : Base {}

[333fred]

Language design is rarely that absolute on what people would expect, or what would be a good idea. My initial reaction on seeing this was exactly what I wrote 🙂.

[CyrusNajmabadi]

Mine too, fwiw. Hence using 'class', which I felt properly distanced itself from 'this=instance' semantics.

[TahirAhmadov]

To me, the typeof is such a strong indication that this is compile-time type and not runtime instance, that I would never think this indicates it's runtime somehow.

[theunrepentantgeek]

Is there an existing proposal to allow generic parameters to use class to reference the current class?

Because it seems to me that it would be even clearer if the original suggestion was

private static readonly ILog _log = LogManager.GetLogger<MyClass>();

with a potential rewrite to:

private static readonly ILog _log = LogManager.GetLogger<class>();

Actually, I just realized: The implentation of LogManager.GetLogger<T>(); could include (for DEBUG builds only) a check using MethodBase.GetCurrentMethod() to verify that T is in the current inheritance hierarchy. This doesn't address the need for the code to be updated after copy/paste - but it does prevent the error from going undetected, and without any performance penalty at runtime.

[LWChris]

Using 'class' felt properly distanced from 'this=instance' semantics.

At first I agreed when reading that.

But then I thought - if I expected "Derived" when writing typeof(this), would I expect "Base" when writing typeof(class)? And I felt like the answer would still be "no".

The quickest description of typeof(...) that came to my mind was "static .GetType()". But if I was expecting "Derived", that would imply I was oblivious to what "static" means. And that would probably be the case for this and class alike. Just a feeling though.

[BlinD-HuNTeR]

Why hasn't anyone written a source generator for this yet? Copy-pasting is a thing of the past now.

[LWChris]

I don't know a lot about source generators yet, but would that mean every class that needs a logger has to be made partial with a static partial ILogger GetLogger() method?

[BlinD-HuNTeR]

I don't know a lot about source generators yet, but would that mean every class that needs a logger has to be made partial with a static partial ILogger GetLogger() method?

For the partial part, yes. But you don't need to have a GetLogger method, you could have the source generator produce the _log field directly.

[TahirAhmadov]

#5261

[LWChris]

Bah. Search doesn't show that one on the first 3 pages... Of course, it is the first entry on page 4. 🙄