C# 12's Secret Feature | .NET Tips 8

[petrusion]

I found this feature by accident. I had to write some empty classes and structs to use with code generators, and I wrote them as I would in Rust, with just the semicolon after the name. A few minutes later when it successfully compiled I thought to myself "Wait, that shouldn't have worked"

[an_wobbly]

Combined with primary constructors and how records have... always worked - this is a change that actually makes a lot of sense.

[promant]

Most people will find them useless, but in fact empty classes do sometimes come in handy. For one, they are often used as 'tags', e.g. in Unity's DOTS or in DI, for two, they work really well with source generation, where the only thing you do is mark it with 'partial' and an attribute and then the magic stuff just happens.

[ethanrushbrook]

Been doing this and it really helps keep the code base clean sometimes. Good feature, should have been around since C# 1.

[jondoty]

One legitimate use I had for an empty class was when I was implementing an API for communicating with a proprietary Bluetooth peripheral. Our library defined “commands”, which were requests the peripheral could fulfill. Each included logic for decoding its response. All commands implemented a common interface with a strongly typed response. But some commands did not return a response. So we made those return a dummy type (i.e. an empty class called NullResponse).

We could have made commands that return no response implement some different interface, but we would have lost the ability to provide APIs that chain commands that return responses intermixed with commands that don’t.

[pi_xi]

Empty types are useful to overload methods. However, named parameters and default values are usually better. Empty interfaces are used to "tag" classes, which is useful when you work with additional preprocessors and auxillary compilers.

[ryan-heath]

Didn’t know {} was previously mandatory.
Used ; recently to create a marker interface. It felt just natural.

[cward]

Use this all the time for marker interfaces and records (esp. commands/events). So much tidier!

[nitrous]

Really useful when you interop with unmanaged code and you need strongly typed opaque pointers.

[Kitulous]

it's been introduced for records but very useful for other types as well

[markovcd]

I use empty types all the time, it's for event driven system - sometimes the event doe not have any additional data with it.

[funkydiddykong]

This seems good, I use empty structs a lot for typing pointers.

[hadahda]

sounds like a bug that slipped by and turned out to be a feature 😂😂

[Shocked_Creative]

yeah i know that function. I use both the brackets and the semicolon.

[asagiai]

Well the no body part is new to me. But isn't empty class always been there? I have been using it for quite a while.

[vothaison]

i have so many empty sub classes in my code waiting for such a feature.

[ronsijm]

Since we have file scoped name spaces, can we have file scoped classes already...?

[MahbuburRahman-ucnp]

I just used this last week, didn't even realize it did not exist in C#11.

[ed-jamal]

I figured it out on my own. I was curious what would happen if I swapped out those curly brackets for a semicolon.

[Sergio_Loureiro]

I don't ever remember see a case where an empty class / struct / interface would be useful. Perhaps code generators?