On Monday, 12 March 2018 at 02:44:17 UTC, Joe wrote:
I saw the extern(C) and I believe I tried it before my previous post, but dismissed it because I saw no difference in compiler behavior.
Yeah, the compiler should just tell you what specifically it is complaining about instead of making you hunt. These "no function match" errors are actually my #1 pain point as a daily D user... and as a regular D tech support rep, I see there are very frequent problems for everyone else too.
Could you explain or direct me to something that elucidates why the "scope" qualifiers are needed? And is there something else that is necessary inside compar() or are the "scope"s just for decorative purposes?
So `scope` means you promise not to escape the reference outside your scope; that you won't store the pointers somewhere else for future use.
It is defined here: https://dlang.org/spec/function.html#parameters tho that's pretty light.
The compiler only checks it if you throw some random -dipsomething switch. The idea is something similar to Rust's borrow checker. It aims to make it a compile error to sneak out pointers to temporaries through our callback. You wouldn't do that anyway with a compare function, but now it is an error to try ( if the strict enforcement thing is thrown. and i don't remember the name, they are all random dip numbers on the switches)
I'm actually mildly against adding these directly to C functions, but this attribute spam is being added to all the druntime definitions. It requires stuff like nothrow and nogc on a bunch of handlers too, ugh, but the idea behind it is to make sure you don't break the C function's documented rules, but here checked by the D compiler without needing any runtime wrappers/checks.
But until recently it wasn't checked at all which is why I wasn't sure if that was causing your error. I guess it is required to match the function call even if the strict enforcement isn't thrown now.
