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
FnMut) into an
ordinary C function pointer that we can pass as a callback to C.
Building libffi will build lifbffi-sys, which will in turn build the libffi C library from github, which requires that you have a working make, C compiler, automake, autoconf, and texinfo first. It’s on crates.io, so you can add
[dependencies] libffi = "0.6.4"
extern crate libffi;
to your crate root.
This crate supports Rust version 1.20 and later.
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.
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));