std::mem

Trait SizedTypeProperties

Source 
#[doc(hidden)] pub trait SizedTypeProperties: Sized {
    #[doc(hidden)] const IS_ZST: bool = _;
    #[doc(hidden)] const LAYOUT: Layout = _;
    #[doc(hidden)] const MAX_SLICE_LEN: usize = _;
}
🔬This is a nightly-only experimental API. (sized_type_properties)
Expand description

Provides associated constants for various useful properties of types, to give them a canonical form in our code and make them easier to read.

This is here only to simplify all the ZST checks we need in the library. It’s not on a stabilization track right now.

Provided Associated Constants§

Source

#[doc(hidden)] const IS_ZST: bool = _

🔬This is a nightly-only experimental API. (sized_type_properties)

true if this type requires no storage. false if its size is greater than zero.

§Examples
#![feature(sized_type_properties)]
use core::mem::SizedTypeProperties;

fn do_something_with<T>() {
    if T::IS_ZST {
        // ... special approach ...
    } else {
        // ... the normal thing ...
    }
}

struct MyUnit;
assert!(MyUnit::IS_ZST);

// For negative checks, consider using UFCS to emphasize the negation
assert!(!<i32>::IS_ZST);
// As it can sometimes hide in the type otherwise
assert!(!String::IS_ZST);
Source

#[doc(hidden)] const LAYOUT: Layout = _

🔬This is a nightly-only experimental API. (sized_type_properties)
Source

#[doc(hidden)] const MAX_SLICE_LEN: usize = _

🔬This is a nightly-only experimental API. (sized_type_properties)

The largest safe length for a [Self].

Anything larger than this would make size_of_val overflow isize::MAX, which is never allowed for a single object.

Dyn Compatibility§

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementors§