Trait objc2::encode::OptionEncode
source · pub unsafe trait OptionEncode { }Expand description
A helper trait for types that are encodable inside an Option.
See the nomicon for details on which types uphold this promise.
This is 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 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);