4 ms·

Kotlin managed it in some cases with clever forwards compatible type system tricks, so it's not impossible

pjmlp 4y ago
Except it does so by compiling into the same bytecode as Java, javap will just output Java like code from class files, and some stuff like co-routines cannot be called from existing Java code without wrappers that setup the runtime semantics as expected by Kotlin libraries.
- fidgewidge 4y ago
  Yes, but so? When they can implement a feature in a forwards compatible way they do, when they can't, they don't and it's caveated as such. That's why nullable types and other Kotlin specific type stuff are encoded using annotations. It's the same strategy here. Carbon is (was?) also intended to compile to the C++ ABI and so does Circle, that's why it says it doesn't run on Windows (commercially a huge error. many of the biggest C++ codebases that could benefit are running on Windows like game engines, and Windows doesn't impose a specific C++ ABI anyway). But there's no way to take existing code files and switch them to the new language in Carbon, at least not yet. Kotlin was carefully designed at every step of the way such that every Java program can be expressed in Kotlin without change, even if that meant compromising on some things. Seems like the Carbon guys are being sucked up by the lure of safetyism and just want to make their own version of Rust that happens to compile to the Itanium C++ ABI.
  - pjmlp 4y ago
    It is only forward compatible, is stuck in decisions when Java 8 was current, there is no roadmap to keep the language in sync wiht the underlying progress of the platform as Kotlin tries to be everywhere. Loom, value types, SIMD, Panama,... are all features that start to be an issue to expose as Kotlin features. It is working on Android, because Google is pushing it as Java 8 => Kotlin, not as Java XYZ <=> Kotlin.
    - fidgewidge 4y ago
      Loom doesn't need to pose any issues for Kotlin. If you target only the JVM, you just use virtual threads directly and ignore the coroutines stuff. If you target other runtimes you use them. If you use a KMP library, just surround stuff marked async with runBlocking {}. SIMD/Panama stuff is just new APIs. No problem there. Kotlin maybe even wins because Panama is super verbose. JVM value types seems never to arrive. Stuck in dev hell for years maybe. If/when it ever does see the light of day, Kotlin has value types and so it can just be compiled to a JVM value type to get the benefits. You'd need to opt in to an ABI break but no big deal. So the binary compatibility part hardly seems an issue even looking forward a long way into the future. It's probably harder for C++ because the language there seems to evolve quicker than Java!
      - pjmlp 4y ago
        What Kotlin calls value types aren't the real deal, just syntax sugar for primitive types with method with a single field. KMP taken to the extreme, is better for Kotlin just to do its own thing with Kotlin/Native, except it is so behind that JetBrains is using Rust instead for Fleet services. Java is expected to have language level support for some of those features, will Kotlin catch up?
  - seanbax 4y ago
    I'd like to target Windows. Windows does impose a specific C++ ABI, but it's completely undocumented. It's really just whatever Visual C++ does. C++ ABI is very complex, especially vtable layout and RTTI and EH. I am looking to get Microsoft's assistance on targeting Windows. It's a priority, but they don't want to help yet.
    - fidgewidge 4y ago
      Isn't that what com is for? Win32 is compiler agnostic.
      - seanbax 4y ago
        https://itanium-cxx-abi.github.io/cxx-abi/abi.html https://itanium-cxx-abi.github.io/cxx-abi/abi.html See all the stuff there? exceptions, vtable layout, rtti, mangling, etc. There's a Windows equivalent for all of that. That's what I want access to.
        fidgewidge 4y ago
        Right I know what a C++ ABI is but I still don't get it. To write C++ apps on Linux you need to match the ABI because there are lots of raw libraries that are just straight compiled C++. On Windows it's not like that outside of the VC++ runtime itself. Everything is C APIs or COM, and wrappers around that. MS never documented their C++ ABI because as far as they're concerned it's not something anyone needs to know, in order to write Windows apps or have components/libraries interop with each other. They never expose raw C++ objects in Windows. When they have C++ APIs they come as source or headers.

Except it does so by compiling into the same bytecode as Java, javap will just output Java like code from class files, and some stuff like co-routines cannot be called from existing Java code without wrappers that setup the runtime semantics as expected by Kotlin libraries.

fidgewidge 4y ago
Yes, but so? When they can implement a feature in a forwards compatible way they do, when they can't, they don't and it's caveated as such. That's why nullable types and other Kotlin specific type stuff are encoded using annotations. It's the same strategy here. Carbon is (was?) also intended to compile to the C++ ABI and so does Circle, that's why it says it doesn't run on Windows (commercially a huge error. many of the biggest C++ codebases that could benefit are running on Windows like game engines, and Windows doesn't impose a specific C++ ABI anyway). But there's no way to take existing code files and switch them to the new language in Carbon, at least not yet. Kotlin was carefully designed at every step of the way such that every Java program can be expressed in Kotlin without change, even if that meant compromising on some things. Seems like the Carbon guys are being sucked up by the lure of safetyism and just want to make their own version of Rust that happens to compile to the Itanium C++ ABI.
- pjmlp 4y ago
  It is only forward compatible, is stuck in decisions when Java 8 was current, there is no roadmap to keep the language in sync wiht the underlying progress of the platform as Kotlin tries to be everywhere. Loom, value types, SIMD, Panama,... are all features that start to be an issue to expose as Kotlin features. It is working on Android, because Google is pushing it as Java 8 => Kotlin, not as Java XYZ <=> Kotlin.
  - fidgewidge 4y ago
    Loom doesn't need to pose any issues for Kotlin. If you target only the JVM, you just use virtual threads directly and ignore the coroutines stuff. If you target other runtimes you use them. If you use a KMP library, just surround stuff marked async with runBlocking {}. SIMD/Panama stuff is just new APIs. No problem there. Kotlin maybe even wins because Panama is super verbose. JVM value types seems never to arrive. Stuck in dev hell for years maybe. If/when it ever does see the light of day, Kotlin has value types and so it can just be compiled to a JVM value type to get the benefits. You'd need to opt in to an ABI break but no big deal. So the binary compatibility part hardly seems an issue even looking forward a long way into the future. It's probably harder for C++ because the language there seems to evolve quicker than Java!
    - pjmlp 4y ago
      What Kotlin calls value types aren't the real deal, just syntax sugar for primitive types with method with a single field. KMP taken to the extreme, is better for Kotlin just to do its own thing with Kotlin/Native, except it is so behind that JetBrains is using Rust instead for Fleet services. Java is expected to have language level support for some of those features, will Kotlin catch up?
- seanbax 4y ago
  I'd like to target Windows. Windows does impose a specific C++ ABI, but it's completely undocumented. It's really just whatever Visual C++ does. C++ ABI is very complex, especially vtable layout and RTTI and EH. I am looking to get Microsoft's assistance on targeting Windows. It's a priority, but they don't want to help yet.
  - fidgewidge 4y ago
    Isn't that what com is for? Win32 is compiler agnostic.
    - seanbax 4y ago
      https://itanium-cxx-abi.github.io/cxx-abi/abi.html https://itanium-cxx-abi.github.io/cxx-abi/abi.html See all the stuff there? exceptions, vtable layout, rtti, mangling, etc. There's a Windows equivalent for all of that. That's what I want access to.
      - fidgewidge 4y ago
        Right I know what a C++ ABI is but I still don't get it. To write C++ apps on Linux you need to match the ABI because there are lots of raw libraries that are just straight compiled C++. On Windows it's not like that outside of the VC++ runtime itself. Everything is C APIs or COM, and wrappers around that. MS never documented their C++ ABI because as far as they're concerned it's not something anyone needs to know, in order to write Windows apps or have components/libraries interop with each other. They never expose raw C++ objects in Windows. When they have C++ APIs they come as source or headers.