peak bear
Hello! am using Lua C library directly by translating and building from source.
But the translated file contains NULL defined as follows:
pub const NULL = @import("std").zig.c_translation.cast(?*anyopaque, @as(c_int, 0));
but that results in the error shown in the image.
but changing its value to
pub const NULL = null;
works just fine!
Any thoughts?
glass plinth
C functions which get translated by translate-c (either explicitly on the command line or automatically with @cImport()) that have pointer parameters always get the ?[*c] pointer type, as described in https://ziglang.org/documentation/master/#C-Pointers . If you want more info on that, I'm happy to explain, but it's a way to deal with C's more limited type system.
The NULL const that was generated was translated from stddef.h, I believe, which is included from Lua's headers. Now, you don't actually want to use that value when passing a null pointer to a function in Zig, you would want to pass Zig's null as you did, which satisfies the ?[*c] parameters, or any optional parameter.
That std.zig.c_translation.cast function is casting to ?*anyopaque, as the error message shows, which won't be accepted by a function expecting a [*c]const u8. The NULL definition there isn't actually useful, it just needs to be there in case it is referenced.
Basically:
NULL because it has to, but it is given the most vague definition possible so that you would be forced to cast it to something before using it — don't use it!?[*c]T for pointer params, even if they are expected to be non-null, because of C type system being less precise than Zig'snull to pass a null pointer to a translated C functionHope that helps!
peak bear
Basically:
* translate-c created a declaration for that C `NULL` because it has ...
Oh I guess I know what's going wrong here. am not using NULL myself.
But am using a translated macro that seems to use it
glass plinth
Oh snap, is it a Lua macro? In my experience I had to basically translate by hand any Lua macro I wanted to use
peak bear
Oh snap, is it a Lua macro? In my experience I had to basically translate by han...
yeeep
glass plinth
Which one if I may ask? And which Lua version?
peak bear
master
am building from source
luaL_dofile
I guess am just going to do it without macros by checking the macros source code
glass plinth
That's the best way
glass plinth
Or you could have a look at https://github.com/natecraddock/ziglua
peak bear
I'd like to roll my own, so when something happens, I know what's wrong
glass plinth
(Soon will integrate with the zig package manager)
peak bear
also am using git submodules
glass plinth
As you wish. I did the same, it's such a small API it doesn't matter
peak bear
As you wish. I did the same, it's such a small API it doesn't matter
is that btw the whole API?
and is it automated?
glass plinth
It's the whole API for Lua versions 5.1 through 5.4 (no LuaJIT). As far as I know it's hand-written. The author is on this discord and has a thread in #1024381264213594242 if you need to get in touch
It's quite nicer than using the translate-c output directly, too
(Actually I do know it's hand-written, there are lots of cleanups and manual macro translations applied)
peak bear
yea I see. currently I try to stay away from the zig ecosystem as it looks a bit immature
glass plinth
ziglua is an example of a well-done Zig library, in my personal opinion. Also actively maintained
but I understand your hesitation, it's still the wild west
peak bear
btw I'm also using a custom zig script that translates the headers so I have autocomplete
lol
so I guess I might as well search for the line that starts with pub const NULL = and replace it with null
before even savinig the generated file
but am not sure if that's enough to make all macros work
glass plinth
It kind of sounds like you are doing what has already been done in ziglua. I don't mean to say it's a bad thing, but there was a lot of good quality work done on that side that you might find useful. Unless your goal is learning to DIY of course, then it doesn't necessarily apply :)
glass plinth
Yep, and there are good reasons for that. C macros being one of them. But there are others, such as adding a wrapper type that can convert between Zig's Allocator interface and Lua's allocator interface, which can't be automated with a script
(Then again, I'm generally not a user or fan of auto-binding systems...aside from translate-c, so please do take my thoughts as having that bias)
peak bear
well thanks for the info tho, I may try those bindings on the side and see if they work for me
glass plinth
For sure, either way I'm happy there is another Lua user in the chat!