Trait objc2::encode::OptionEncode
source · pub unsafe trait OptionEncode { }Expand description
A helper trait for types that follow the “null pointer optimization”, and
are encodable inside an Option.
See the Option documentation for details on which types
this holds for, and the nomicon for more details on the
null pointer optimization.
This trait used to work around the orphan rule, which would normally
prevent you from implementing Encode/RefEncode for
Option<CustomType>.
§Safety
You must ensure that the implemented type T has the same layout and
function call ABI as Option<T>.
§Examples
use objc2::encode::{Encode, Encoding, OptionEncode};
use core::ptr::NonNull;
use core::ffi::c_void;
#[repr(transparent)]
struct MyBlockType(NonNull<c_void>);
// SAFETY: `MyBlockType` is meant to represent a pointer to a block
unsafe impl Encode for MyBlockType {
const ENCODING: Encoding = Encoding::Block;
}
// SAFETY: `MyBlockType` is `repr(transparent)` over `NonNull`, which
// means that `Option<MyBlockType>` has the same layout.
unsafe impl OptionEncode for MyBlockType {}
assert_eq!(<Option<MyBlockType>>::ENCODING, MyBlockType::ENCODING);