The C libffi library provides two main facilities: assembling calls
to functions dynamically, and creating closures that can be called
as ordinary C functions. In Rust, the latter means that we can turn
a Rust lambda (or any object implementing Fn/FnMut) into an
ordinary C function pointer that we can pass as a callback to C.
The easiest way to use this library is via the high layer module, but
more flexibility (and less checking) is provided by the middle and
low layers.
It’s on crates.io, so it can be
used by adding libffi to the dependencies in your project’s
Cargo.toml:
toml
[dependencies]
libffi = "0.1"
It is necessary to have C libffi installed first. (We’ve tested with libffi version 3.2.1.)
In this example, we convert a Rust lambda containing a free variable
into an ordinary C code pointer. The type of fun below is
extern "C" fn(u64, u64) -> u64.
```rust use libffi::high::Closure2;
let x = 5u64; let f = |y: u64, z: u64| x + y + z;
let closure = Closure2::new(&f); let fun = closure.code_ptr();
assert_eq!(18, fun(6, 7)); ```
I’m writing this section to document my build process.
Installed pkg-config: brew install pkg-config
Installed libffi 3.2.1 (rather than OS X system libffi, which is old)
Installed bindgen 0.18.0