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Make *const (), *mut () okay for FFI by dtolnay · Pull Request #84267 · rust-lan...

 2 years ago
source link: https://github.com/rust-lang/rust/pull/84267
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dtolnay commented on Apr 17

Pointer-to-() is used occasionally in the standard library to mean "pointer to none-of-your-business". Examples:

I believe it's useful for the same purpose in FFI signatures, even while () itself is not FFI safe. The following should be allowed:

extern "C" {
    fn demo(pc: *const (), pm: *mut ());
}

Prior to this PR, those pointers were not considered okay for an extern signature.

warning: `extern` block uses type `()`, which is not FFI-safe
 --> src/main.rs:2:17
  |
2 |     fn demo(pc: *const (), pm: *mut ());
  |                 ^^^^^^^^^ not FFI-safe
  |
  = note: `#[warn(improper_ctypes)]` on by default
  = help: consider using a struct instead
  = note: tuples have unspecified layout

warning: `extern` block uses type `()`, which is not FFI-safe
 --> src/main.rs:2:32
  |
2 |     fn demo(pc: *const (), pm: *mut ());
  |                                ^^^^^^^ not FFI-safe
  |
  = help: consider using a struct instead
  = note: tuples have unspecified layout

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