# Interop with other crates
The `objc2` project provides bindings for a lot of frameworks, including many existing popular framework crates. A few examples are given in the table below, see the full list [here][all-crates].
| [`core-foundation`](https://docs.rs/core-foundation) | [`objc2-core-foundation`](https://docs.rs/objc2-core-foundation) |
| [`core-graphics`](https://docs.rs/core-graphics) | [`objc2-core-graphics`](https://docs.rs/objc2-core-graphics) |
| [`security-framework`](https://docs.rs/security-framework) | [`objc2-security`](https://docs.rs/objc2-security) |
| [`system-configuration`](https://docs.rs/system-configuration) | [`objc2-system-configuration`](https://docs.rs/objc2-system-configuration) |
| [`cocoa-foundation`](https://docs.rs/cocoa-foundation) | [`objc2-foundation`](https://docs.rs/objc2-foundation) |
| [`cocoa`](https://docs.rs/cocoa) | [`objc2-app-kit`](https://docs.rs/objc2-app-kit) |
| [`coremidi`](https://docs.rs/coremidi) | [`objc2-core-midi`](https://docs.rs/objc2-core-midi) |
| [`core-video-sys`](https://docs.rs/core-video-sys) | [`objc2-core-video`](https://docs.rs/objc2-core-video) |
While it is recommended that you use the `objc2` crates, you may still in certain cases want to use the existing crates. This can be a bit cumbersome, since `objc2` and [`block2`] impose certain requirements on the types involved, see below.
[all-crates]: crate::topics::about_generated::list
[`block2`]: https://docs.rs/block2/latest/block2/
## Implementing `Encode` for a newtype wrapper
Due to Rust's orphan rules, `core-foundation` types do not implement `Encode`, and as such cannot be passed to/from methods and in blocks by default.
We're (slowly) working on fixing this, see [servo/core-foundation-rs#628], but in the meantime, you can use a newtype wrapper around the `CF...Ref`, and implement [`Encode`] for that wrapper.
[servo/core-foundation-rs#628]: https://github.com/servo/core-foundation-rs/pull/628
[`Encode`]: crate::encode::Encode
### Examples
Declaring an external function to [`CFRunLoopObserverCreateWithHandler`](https://developer.apple.com/documentation/corefoundation/1542816-cfrunloopobservercreatewithhandl?language=objc), which uses blocks and `block2`, and as such require its parameters to implement `Encode`.
```rust
use std::ptr;
use block2::{RcBlock, Block};
use core_foundation::base::{Boolean, CFAllocatorRef, CFIndex, CFOptionFlags, TCFType};
use core_foundation::runloop::{CFRunLoopActivity, CFRunLoopObserver, CFRunLoopObserverRef, kCFRunLoopAllActivities};
use objc2::encode::{Encode, Encoding};
#[repr(transparent)]
struct CFRunLoopObserverRefWrapper(CFRunLoopObserverRef);
// SAFETY: `CFRunLoopObserverRefWrapper` is `#[repr(transparent)]` over
// `CFRunLoopObserverRef`, which is a typedef to `struct __CFRunLoopObserver *`.
unsafe impl Encode for CFRunLoopObserverRefWrapper {
const ENCODING: Encoding = Encoding::Pointer(&Encoding::Struct("__CFRunLoopObserver", &[]));
}
extern "C" {
fn CFRunLoopObserverCreateWithHandler(
allocator: CFAllocatorRef,
activities: CFOptionFlags,
repeats: Boolean,
order: CFIndex,
block: &Block<dyn Fn(CFRunLoopObserverRefWrapper, CFRunLoopActivity)>
) -> CFRunLoopObserverRef;
}
let observer = observer.0;
});
let observer = unsafe {
CFRunLoopObserver::wrap_under_create_rule(CFRunLoopObserverCreateWithHandler(
ptr::null(),
kCFRunLoopAllActivities,
false as Boolean,
0,
&block,
))
};
#
# assert!(CFRunLoopObserverRefWrapper::ENCODING.equivalent_to_str("^{__CFRunLoopObserver=}"));
```
An alternative, if you don't want to go through the trouble of creating a newtype, is to use the `"relax-void-encoding"` Cargo feature.
Here we set the [`-[CALayer borderColor]`](https://developer.apple.com/documentation/quartzcore/calayer/1410903-bordercolor?language=objc) property (which uses `CGColorRef`).
```rust, ignore
use core_foundation::base::ToVoid;
use core_graphics::color::CGColor;
use objc2_quartz_core::CALayer;
use objc2::msg_send;
fn set_border_color(layer: &CALayer, color: &CGColor) {
let color = color.to_void();
// Passing `*const c_void` here requires the "relax-void-encoding" feature
unsafe { msg_send![layer, setBorderColor: color] }
}
let layer = unsafe { CALayer::new() };
let color = CGColor::rgb(1.0, 0.0, 0.0, 1.0);
set_border_color(&layer, &color);
```
## Toll-free bridging
Certain CoreFoundation types are documented to be ["toll-free bridged"], which means that they're completely interoperable with the Foundation types. To convert between these in Rust, you'll have to cast the pointers, e.g. between `CFStringRef` and `*const NSString`.
["toll-free bridged"]: https://developer.apple.com/library/archive/documentation/CoreFoundation/Conceptual/CFDesignConcepts/Articles/tollFreeBridgedTypes.html
### Example
Toll-free bridging between `CFString` and `NSString`.
```rust
use core_foundation::base::TCFType;
use core_foundation::string::{CFString, CFStringRef};
use objc2_foundation::{NSString, ns_string};
use objc2::rc::Retained;
fn cf_string_to_ns(s: &CFString) -> &NSString {
let ptr: CFStringRef = s.as_concrete_TypeRef();
let ptr: *const NSString = ptr.cast();
// SAFETY: CFString is toll-free bridged with NSString.
unsafe { ptr.as_ref().unwrap() }
}
// Note: The `core_foundation` crate does not allow zero-cost (non-owning)
// references to objects, so we have to convert from a `Retained<NSString>` to
// the owning `CFString` (i.e. `&NSString -> &CFString` is not possible).
fn ns_string_to_cf(s: Retained<NSString>) -> CFString {
// Yield ownership over the string
let ptr: *const NSString = Retained::into_raw(s);
let ptr: CFStringRef = ptr.cast();
// SAFETY: NSString is toll-free bridged with CFString, and
// ownership was passed above with `Retained::into_raw`.
unsafe { CFString::wrap_under_create_rule(ptr) }
}
let cf = CFString::new("foo");
let ns = NSString::from_str("foo");
assert_eq!(cf_string_to_ns(&cf), &*ns);
assert_eq!(cf, ns_string_to_cf(ns));
```