Pointers Are More Abstract Than You Might Expect in C

Re:Pointers Are More Abstract Than You Might Expect in C by cryptonector on Monday July 02, 2018 @01:12PM (#17443479)

The only thing I ask of any C-replacement languages is that they make it possible to describe ABIs, message layouts, and on-disk formats in detail. C historically does that well enough, though not really all that well (e.g., bitfields and enums have issues, and struct packing is not always easy to get right). There is a lot of value to this!

The ability to mix object code from multiple languages (FFI) is critical, and that's why C is the common denominator for FFIs.

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Re:Pointers Are More Abstract Than You Might Expect in C by bluejekyll on Monday July 02, 2018 @01:30PM (#17443665)

I won't do this justice, so I'll point you to the Rust book on this subject: https://doc.rust-lang.org/book/second-edition/ch19-01-unsafe...

In short, at the moment, if you want a stable ABI, you must export an un_mangled C interface. This is easy enough. One of my favorite sites is this for FFI stuff: http://jakegoulding.com/rust-ffi-omnibus/

It covers a bunch of languages, and suggests techniques for overcoming any complexity in exposing higher order types.

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Re:Pointers Are More Abstract Than You Might Expect in C by cryptonector on Tuesday July 03, 2018 @01:57AM (#17447888)

I wasn't criticizing Rust, and I'm aware of what you linked. The point I was making is that this sort of functionality is a sine qua non for C-replacement languages. That Rust has it is to its credit, and one reason that I think it is a very good C-replacement language.

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Re:Pointers Are More Abstract Than You Might Expect in C by pjmlp on Monday July 02, 2018 @01:30PM (#17443673)

C is the common denominator for FFI for OS that happen to be written in straight C, which then mix the C ABI with OS ABI.

That is not true in mainframes, Windows (ongoing replacement of Win32 with COM, it is lot of fun to do COM in C, more so UWP), Android (JNI, AIDL), Web (JavaScript/WebAssembly), iOS/macOS (Objective-C runtime), Fuchsia (IDL).

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Re:Pointers Are More Abstract Than You Might Expect in C by cryptonector on Monday July 02, 2018 @05:47PM (#17445596)

Re: COM, that works because MSFT can a) commit to an ABI for C++, b) they can stick to a subset of C++ that makes that easy enough. Similarly for OS X.

The point isn't to stay in a C-like world. The point is that it must be possible to specify an ABI, file formats, and so on, in the host language. Yes, we can use external IDLs (even user them as DSLs if you like). I know all about and have worked with quite a lot of them (e.g., ASN.1, XDR, and many many others). But when you get down to a certain level, a light-weight approach really pays off. For example, at the system call level, and for many sufficiently simple file formats and such. At a higher end in complexity, on the other hand, then ASN.1 and friends pay off instead, mostly in a) obtaining interoperability with implementations written in other languages, b) managing extensibility.

Another thing is that some of us think about how things work at many levels. It's nice to be able to think about an interface and accurately picture what goes on at a low layer. It's difficult to do that with HLLs. But HLLs can easily have features that allow fine-grained control of or exposure of low level details, and that's what I'm saying I want to have as an option.

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Re:Pointers Are More Abstract Than You Might Expect in C by int_19h on Monday July 02, 2018 @03:19PM (#17444590)

COM and WinRT are still based on the C ABI though. So anything that can do that, can do them - hopefully with more layers on top for convenience sake, of course...

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Re:Pointers Are More Abstract Than You Might Expect in C by pjmlp on Monday July 02, 2018 @04:43PM (#17445182)

Not quite, COM yes, although it is masochistic to do so without any higher level help.

UWP on the other hand extends COM to support inheritance and value types across calls, and the lowest Microsoft was willing to go on their high performance components was the Windows Runtime C++ Template Library, now replaced by C++/WinRT bindings and updated MIDL compiler.

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Re:Pointers Are More Abstract Than You Might Expect in C by int_19h on Thursday July 05, 2018 @03:49AM (#17461557)

The ABI is still C. Value types are just structs, and inheritance is implemented via aggregation - under the hood, it's all just interfaces and conventions on how they all play together. So any language that can do C FFI, can do WinRT. We did most of it with Python and ctypes as a prototype.

And you could even use that from C back in the day if you #included the "Windows.*.h" headers that shipped with the SDK - they had a bunch of #ifdef __cplusplus etc in them. Not sure if that stuff is still there or not.

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