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This post is auto-generated from RSS feed The Rust Programming Language Forum - Latest topics. Source: Can't read &[MyType(u8)] from &[u8] with Zerocopy

I'm trying to write a Vec of my u8 wrapper type into bytes and then use ref_from_bytes/prefix/suffix, but it won't compile.

I had the compiler demand KnownLayout for another struct, but adding a derive macro there worked and fixed it. Here instead, it won't.

use zerocopy::{FromBytes, Immutable, IntoBytes, KnownLayout};

#[derive(Clone, Debug, FromBytes, IntoBytes, Immutable, KnownLayout)]
pub struct Cost(pub u8);

fn main() {
	let costs = vec![Cost(10), Cost(20), Cost(30), Cost(40), Cost(50), Cost(60), Cost(70), Cost(80), Cost(90), Cost(100)];
	
	let mut data: Vec<u8> = vec![]; // vec![0; 16];
	println!("data before: {:?}", data);
	costs.write_to_io(&mut data).unwrap();
	println!("data after: {:?}", data);

	let (c2, data3) = Cost::ref_from_prefix_with_elems(&data, 10).unwrap();
}

The error:

error[E0271]: type mismatch resolving `<Cost as KnownLayout>::PointerMetadata == usize`
    --> src/main.rs:37:20
     |
37   |     let (c2, data3) = Cost::ref_from_prefix_with_elems(&data, 10).unwrap();
     |                       ^^^^ type mismatch resolving `<Cost as KnownLayout>::PointerMetadata == usize`
     |
note: expected this to be `usize`
    --> src/main.rs:6:57
     |
6    | #[derive(Clone, Debug, FromBytes, IntoBytes, Immutable, KnownLayout)]
     |                                                         ^^^^^^^^^^^
note: required by a bound in `ref_from_prefix_with_elems`
    --> /home/culebron/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/zerocopy-0.8.27/src/lib.rs:4190:27
     |
4185 |     fn ref_from_prefix_with_elems(
     |        -------------------------- required by a bound in this associated function
...
4190 |         Self: KnownLayout<PointerMetadata = usize> + Immutable,
     |                           ^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `FromBytes::ref_from_prefix_with_elems`
     = note: this error originates in the derive macro `KnownLayout` (in Nightly builds, run with -Z macro-backtrace for more info)

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