[sph]

Call it a niche use-case, but every time I had the chance to evaluate Rust, I had to write a function taking a callback, sometimes across to a C library. Every time I have to deal with an Fn/FnOnce/FnMut trait signature, remember if I need to box it with dyn, mayhaps it takes a reference as argument so I also need to deal with lifetimes signatures, then remember the `for<'a>` syntax, then it blows up because I need to add `+ 'static` at the end which still makes no sense to me, then I just rage quit. I am decently handy with (unsafe) Rust, wrote a minimal OS in it, but dealing with function pointers makes me want to carve my eyes out.

C doesn’t even care. You can cast an int to a function pointer if you want.

With Odin it’s taken me like 5 minutes including reading the section of the docs for the first time.

[phalanx104]

`impl Fn/FnOnce/FnMut` don't stand for function pointers, but rather function items in Rust, and as such they are zero sized so Rust can provide optimizations regarding function items specifically at compile time.

They can decay to function pointers (`$(unsafe)? $(extern)? fn($(inp),*) $(-> $(output))?`, example: unsafe extern fn() -> i32), which you can freely cast between function pointers, `*const/mut T` pointers or `usize`s. https://doc.rust-lang.org/reference/types/function-pointer.h...