FFI: Communicating with the Outside World

FFI is how any language actually interactions with the outside world after all, so Gallium has it.

Calling Gallium over C FFI

Gallium functions are normally mangled and thus not visible over FFI (easily).

When marked extern however, they are not mangled, and can be called over FFI.

extern fn add(x: usize, y: usize) -> usize {
    x + y
}

The above function could be called from C++ like so:

extern "C" {
    std::size_t add(std::size_t x, std::size_t y);
}

int main() {
    auto x = add(5, 3);
}

Calling C from Gallium over C FFI

Gallium can also call functions over the C FFI through the use of external blocks.

external {
    fn malloc(size: usize) -> *mut byte
    fn free(ptr: *mut byte) -> void
}

fn use_malloc() {
    let ptr = malloc(512)

    free(ptr)
}

C FFI is actually how print and friends work, they talk over C FFI to some C++ code in the Gallium runtime library.