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, which would normally prevent 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);

Implementations on Foreign Types§

Implementors§