[simonask]

C# has a unique powerful position in the video game space. In almost every other niche, there are better (or just trendier) solutions, but C# is the only major language that actually gives you a combination of features that are important in video games:

- Dynamic runtime with loose coupling and hot reload of code - extremely useful during development.

- Value types. You don't want every Vector4 to be heap allocated when you're doing 3D graphics, because that's going to be absolutely unusable.

- Access to a relatively low-level substrate for basically-native performance when needed - extremely useful when you're trying to actually ship something that runs well.

Taken in isolation, C# isn't best in class for any of them, but no other language offers all three, especially not if you also want things like a really good debugger and great IDE tools.

To my knowledge, Java has none of these features (yet), and they aren't really important in a lot of the areas where Java is popular. But this is why C# in particular is very strong in the video games niche.

[Archit3ch]

> no other language offers all three

Julia. Of course with the added downside that it's not deployable (asterisk here), which is somewhat important for games. IDE and debugger could be better, but at least it doesn't insist on classes like C#.

[kbolino]

I think these are all valid arguments, but I do want to point out that Java is addressing them.

The first bullet is possible with the JetBrainsRuntime, a fork of OpenJDK: https://github.com/JetBrains/JetBrainsRuntime

The second bullet is a headline goal of Project Valhalla, however it is unlikely to be delivered in quite the way that a C# (or Go or Rust etc.) developer might expect. The ideal version would allow any object with purely value semantics [1] to be eligible for heap flattening [2] and/or scalarization [3], but in experimental builds that are currently available, the objects must be from a class marked with the "value" qualifier; importantly, this is considered an optimization and not a guarantee. More details: https://openjdk.org/projects/valhalla/value-objects

The third bullet (IIUC) is addressed with the Foreign Function & Memory API, though I'll admit what I've played around with so far is not nearly as slick as P/Invoke. See e.g. https://openjdk.org/jeps/454

[1] value semantics means: the object is never on either side of an == or != comparison; the equals and hashCode methods are never called, or are overridden and their implementation doesn't rely on object identity; no methods are marked synchronized and the object is never the target of a synchronized block; the wait, notify, and notifyAll methods are never called; the finalize method is not overridden and no cleaner is registered for the object; no phantom or weak references are taken of the object; and probably some other things I can't think of

[2] heap flattening means that an object's representation when stored in another object's field or in an array is reduced to just the object's own fields, removing the overhead from storing references to its class and monitor lock

[3] scalarization means that an object's fields would be stored directly on the stack and passed directly through registers

[WorldMaker]

The third bullet is also presumably referring to C#'s ancient wider support for unsafe { } blocks for low level pointer math as well as the modern tools Span<T> and Memory<T> which are GC-safe low level memory management/access/pointer math tools in modern .NET. Span<T>/Memory<T> is a bit like a modest partial implementation of Rust's borrowing mechanics without changing a lot of how .NET's stack and heap work or compromising as much on .NET's bounds checking guarantees through an interesting dance of C# compiler smarts and .NET JIT smarts.

[kbolino]

The FFM API actually does cover a lot of the same ground, albeit with far worse ergonomics IMO. To wit,

- There is no unsafe block, instead certain operations are "restricted", which currently causes them to emit warnings that can be suppressed on a per-module basis; it seems the warnings will turn into exceptions in the future

- There is no "fixed" statement and frankly nothing like it all, native code is just not allowed to access managed memory period; instead, you set up an arena to be shared between managed and native code

- MemorySegment is kinda like Memory<T>/Span<T> but harder to actually use because Java's type-erased generics are useless here

- Setting up a MemoryLayout to describe a struct is just not as nice as slapping layout attributes on an actual struct

- Working with VarHandle is just way more verbose than working with pointers

[WorldMaker]

> - There is no unsafe block, instead certain operations are "restricted", which currently causes them to emit warnings that can be suppressed on a per-module basis; it seems the warnings will turn into exceptions in the future

Which sounds funny because C# effectively has gone the other direction. .NET's Code Access Security (CAS) used to heavily penalize unsafe blocks (and unchecked blocks, another relative that C# has that I don't think has a direct Java equivalent), limiting how libraries could use such blocks without extra mandatory code signing and permissions, throwing all sorts of weird runtime exceptions in CAS environments with slightly wrong permissions. CAS is mostly gone today so most C# developers only ever really experience compiler warnings and warnings-as-errors when trying to use unsafe (and/or unchecked) blocks. More libraries can use it for low level things than used to. (But also fewer libraries need to now than used to, thanks to Memory<T>/Span<T>.)

> There is no "fixed" statement and frankly nothing like it all, native code is just not allowed to access managed memory period; instead, you set up an arena to be shared between managed and native code

Yeah, this seems to be an area that .NET has a lot of strengths in. Not just the fixed keyword, but also a direct API for GC pinning/unpinning/locking and many sorts of "Unsafe Marshalling" tools to provide direct access to pointers into managed memory for native code. (Named "Unsafe" in this case because they warrant careful consideration before using them, not because they rely on unsafe blocks of code.)

> MemorySegment is kinda like Memory<T>/Span<T> but harder to actually use because Java's type-erased generics are useless here

It's the ease of use that really makes Memory<T>/Span<T> shine. It's a lot more generally useful throughout the .NET ecosystem (beyond just "foreign function interfaces") to the point where a large swathe of the BCL (Base Class Library; standard library) uses Span<T> in one fashion or another for easy performance improvements (especially with the C# compiler quietly preferring Span<T>/ReadOnlySpan<T> overloads of functions over almost any other data type, when available). Span<T> has been a "quiet performance revolution" under the hood of a lot of core libraries in .NET, especially just about anything involving string searching, parsing, or manipulation. Almost none of those gains have anything to do with calling into native code and many of those performance gains have also been achieved by eliminating native code (and the overhead of transitions to/from it) by moving performance-optimized algorithms that were easier to do unsafely in native code into "safe" C#.

It's really cool what has been going on with Span<T>. It's really wild some of the micro-benchmarks of before/after Span<T> migrations.

Related to the overall topic, it's said Span<T> is one of the reasons Unity wants to push faster to modern .NET, but Unity still has a ways to go to where it uses enough of the .NET coreclr memory model to take real advantage of it.

[simonask]

Yeah, coming to C# from Rust (in a project using both), I’ve been extremely impressed by the capabilities of Span<T> and friends.

I’m finding that a lot of code that would traditionally need to be implemented in C++ or Rust can now be implemented in C# at no or very little performance cost.

I’m still using Rust for certain areas where the C# type system is too limited, or where the borrow checker is a godsend, but the cooperation between these languages is really smooth.