https://github.com/williamvenner/null_fn

✨ A proc attribute macro that allows for creating null function pointers in statics
https://github.com/williamvenner/null_fn

ffi fn function macro null pointer pointers proc-macro proc-macro-attributes ptr rust unsafe

Last synced: 26 days ago
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✨ A proc attribute macro that allows for creating null function pointers in statics

• Host: GitHub
• URL: https://github.com/williamvenner/null_fn
• Owner: WilliamVenner
• License: mit
• Created: 2021-09-23T23:07:00.000Z (about 3 years ago)
• Default Branch: master
• Last Pushed: 2021-09-24T00:31:02.000Z (about 3 years ago)
• Last Synced: 2024-10-11T11:33:28.129Z (about 1 month ago)
• Topics: ffi, fn, function, macro, null, pointer, pointers, proc-macro, proc-macro-attributes, ptr, rust, unsafe
• Language: Rust
• Homepage: https://crates.io/crates/null_fn
• Size: 4.88 KB
• Stars: 1
• Watchers: 3
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
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# ✨ `null_fn`

A proc attribute macro that allows for creating null function pointers in `static`s.

This crate is **unsafe and easy to cause UB with**, `Option` is [FFI safe](https://doc.rust-lang.org/nomicon/ffi.html#the-nullable-pointer-optimization) and may be a more appropriate alternative if you value type safety.

## Example

```rust

static mut UTIL_PlayerByUserId: unsafe extern "C" fn(userid: i32) -> *mut c_void = unsafe { std::mem::transmute::<*const (), _>(std::ptr::null()) }; // error[E0080]: it is undefined behavior to use this value

#[null_fn]

static mut UTIL_PlayerByUserId: unsafe extern "C" fn(userid: i32) -> *mut c_void = std::ptr::null(); // works!

fn main() {

    unsafe {

        UTIL_PlayerByUserId(20); // This would panic, as we have not initialized the function yet. By default the function is set to a small stub function that panics when called.

        UTIL_PlayerByUserId = /* magically find the pointer to the function; sigscan? */;

		// Setting the function's pointer to a null pointer is UB in Rust.

		// https://doc.rust-lang.org/nomicon/ffi.html#the-nullable-pointer-optimization

        let player = UTIL_PlayerByUserId(20); // Now that we set the function pointer, we can call the function without panicking, assuming we found the pointer correctly.

		/* do something with our player! */

    }

}

```