ffi-opaque

A macro generating correct opaque types.

What it does

Until RFC 1861 (Extern types) is implemented, representing opaque structs in Rust is hard, as decribed in the corresponding Nomicon section.

Yet, opaque structs are a common pattern, especially when working with C codebases through FFI.

ffi-opaque provides the opaque! macro which properly generates such types without having to think about the details.

Types generated by this macro are: * are zero-sized * cannot be constructed outside of the module they are defined in * have proper alignment * are !Send, !Sync, !Unpin * are FFI safe

Usage example

Consider this example from the leveldb C API:

```c typedef struct leveldboptionst leveldboptionst;

leveldboptionst* leveldboptionscreate(); ```

It uses an opaque struct to avoid leaking structural details of its database options to a library linking to it. We can represent the opaque struct leveldb_options_t on the Rust side like this:

```rust use ffi_opaque::opaque;

opaque!(leveldboptionst);

extern "C" { pub fn leveldboptionscreate() -> *mut leveldboptionst; } ```

Possible future extensions

If extern types become stabilised, this macro may adopt them.

License

MIT, see LICENSE file.

Acklowledgements