Generating Bindings to Objective-C

bindgen does not (yet) have full Objective-C support, but it can generate bindings for many of the Apple frameworks without too much blocklisting.

In order to generate bindings, you will need -x objective-c as a clang arg. If you'd like to use block you will need -fblocks as a clang arg as well.

Depending on your setup, you may need --generate-block to generate the block function aliases and --block-extern-crate to insert a extern crate block at the beginning of the generated bindings. The same logic applies to the --objc-extern-crate parameter.

The Objective-C classes will be represented as a struct Foo(id) and a trait IFoo where Foo is the Objective-C class and id is an alias for *mut objc::runtime::Object (the pointer to the Objective-C instance). The trait IFoo is needed to allow for the generated inheritance.

Functions that use or return Objective-C pointers of instance Foo will return Foo. The reason this works is because Foo represented as transparent. This will be helpful for many Objective-C frameworks. However, there are some cases where functions return instancetype which is a type alias for id so an occasional foo.0 may be required. An example of this would in the UIKit framework should you want to add a UILabel to a UIStackView you will need to convert the UILabel to a UIView via UIView(label.0).

Each class (struct) has an alloc and a dealloc to match that of some of the alloc methods found in NSObject.

In order to initialize a class Foo, you will have to do something like let foo = Foo(Foo::alloc().initWithStuff()).

To blocklist an Objective-C method, you should add the bindgen generated method path (e.g. IFoo::method or IFoo::class_method) as a blocklist item.

Supported Features

  • Inheritance matched to rust traits with prefixes of I which stands for interface.
  • Protocols which match to rust traits with prefixes of P which stands for Protocol.
  • Classes will generate struct Foo(id) where Foo is the class name and id is a pointer to the Objective-C Object.
  • Blocks

Useful Notes

  • If you‘re targeting aarch64-apple-ios, you’ll need to have the clang arg --target=arm64-apple-ios as mentioned here.
  • The generated bindings will almost certainly have some conflicts so you will have to blocklist a few things. There are a few cases of the parameters being poorly named in the Objective-C headers. But if you‘re using anything with Core Foundation, you’ll find that time.h as has a variable called timezone that conflicts with some of the things in NSCalendar.h.
  • Some small subset of the function headers in the Apple frameworks go against Apple‘s guidelines for parameter names and duplicate the names in the header which won’t compile as mentioned here.
  • instancetype return methods does not return Self for you given class, it returns a mut * objc::runtime::Objc which is aliased as id. This is because Objective-C‘s inheritance doesn’t perfectly match that of Rust's.
  • Depending on what you're trying bindgen against, you may end up including all of Core Foundation and any other frameworks. This will result in a very long compile time.

Not (yet) Supported

  • Nullability attributes which return Options.
  • Probably many other things. Feel free to open an issue.

Example crate(s)