Awhile back, I wrote some C# code that interacts with C/C++ code by reading struct layouts directly. This is unsafe because C structs don't have guaranteed layouts unless you use nonstandard pragmas. So I had the C code bypass regular struct {} and lay out data manually by pointer arithmetic, making it consistent and safe. This worked great, until I discovered that booleans are a different size in C and C++. I fixed this too, but only by doing horrible things I'm only 95% certain actually worked
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@mcc isn’t this what protobuf and frens are for..?
@beatrix *thinks*
Actually… I think protobuf would be a good fit for our situation. I'm not sure why we didn't go with protobuf. I think maybe it's because I thought our needs were simple and protobuf was complicated, but our needs have grown more complex since this project was started.
I just asked the "client", who says that they've actually surveyed C# implementations of Protobuf and as of last survey they all seem to be very hard to use compared to how easy serialization normally is in C#.
@mcc “C structs don’t have guaranteed layouts”
So how does repr(C) work, then? Does it only work with a specific set of compilers? Is it based on platform conventions?
@bytex64 I may be about to say something horribly wrong, but the thing about repr(C) is that it guarantees you are using the same layout as the platform's standard C layout, but DOES NOT convey any information about what this platform is. This means repr(C) can talk to repr(C) but neither one can totally reliably talk to C# which is using pure pointer manipulation.
P/Invoke *can* talk to repr(C)… unless you fall into the hole with the disaster around boolean sizes.
@dotstdy @bytex64 Okay so on the one hand you are entirely right, but on the other hand: Microsoft, creator of this problem, is both the platform defining body who decides the ABI the C compilers are downstream from, AND the author of the currently most common compiler on the platform, AND the body who both defined and implemented the entire C# language
@ireneista @mcc @bytex64 SysV ABI specifies struct layout, and many platforms adopt that?
@rcombs @ireneista @bytex64 I'm not sure what the answer to that question is, but "Oh, it's just Itanium now" seems to have resolved a lot of problems I experienced in the early 00s
@mcc @ireneista @bytex64 the SysV ABI (and its adoption by other unix-like platforms) predates Itanium, though *C++* in particular does use an ABI originally designed for Itanium (which in turn is applied on top of the SysV C ABI for any given platform)
@rcombs @ireneista @bytex64 Honestly the primary compatibility difficulty of my entire adult life is "is Windows doing the same thing as not-Windows, and how can I make Windows do the same thing as not-Windows"
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(There was an additional horrible period in the 00s when I had to think about "is Windows compatible with other copies of Windows" but we seem to have, finally, got past that. In the cyberpunk future Microsoft software can finally talk to Microsoft software.)
I'm thinking about this because I'm having to add to that code right now and it's miserable. I'm not sure why I'm telling you this. I guess I want to stress there are reasons I'm now on team "Nothing but Rust. Nothing but Rust forever. No more C/C++. Rust. What? Okay, Go or Zig are probably fine. Just no C"
@mcc one day someone will invent a C compiler that lets you write C and native Rust together and they will call it Crust
And then... no one will be laughing anymore
@brandonscript this would make me sad
@mcc to be fair if you want layout to be predictable in rust you also need to use C rules...
@mcc The problem is your code won't work on a PDP-10 or a DEC Alpha.
@mcc coders, is this what coding is like?