Trait objc2::Message

source · 
pub unsafe trait Message: RefEncode { }
Expand description

Types that can be sent Objective-C messages.

Implementing this provides MessageReceiver implementations for common pointer types and references to the type, which allows using them as the receiver (first argument) in the msg_send! macro.

This trait also allows the object to be used in rc::Id.

This is a subtrait of RefEncode, meaning the type must also implement that, almost always as Encoding::Object.

Safety

The type must represent an Objective-C object, meaning it:

  • Must be valid to reinterpret as runtime::Object.
  • Must be able to be the receiver of an Objective-C message sent with objc_msgSend or similar.
  • Must respond to the standard memory management retain, release and autorelease messages.

Example

use objc2::runtime::Object;
use objc2::{Encoding, Message, RefEncode};

#[repr(C)]
struct MyObject {
    // This has the exact same layout as `Object`
    inner: Object
}

unsafe impl RefEncode for MyObject {
    const ENCODING_REF: Encoding = Encoding::Object;
}

unsafe impl Message for MyObject {}

// `*mut MyObject` and other pointer/reference types to the object can
// now be used in `msg_send!`
//
// And `Id<MyObject, O>` can now be constructed.

Implementors§