Enum Void

pub enum Void {}

Available on crate feature void only.

Type for impossible situations.

Use this as a type parameter to enums to make the variants that use it unconstructible.

Interaction with unsafe code

It is only valid to convert to Void from other Void-like types, it is undefined behavior to convert from any constructible type, even if zero-sized.

Example, infinite loop which only returns on error.

use core_extensions::{ResultLikeExt, Void};

#[derive(Debug,PartialEq)]
enum Error<T>{
   InvalidItem(T),
   IteratorWasntInfinite,
}

fn reading_numbers<I>(i: I) -> Result<Void, Error<usize>>
where I: IntoIterator<Item = usize>
{
   for elem in i{
       if elem == 0 { return Err(Error::InvalidItem(elem)) }
       println!("{}", elem);
   }
   Err(Error::IteratorWasntInfinite)
}

assert_eq!(reading_numbers(1..100).into_error(), Error::IteratorWasntInfinite);
assert_eq!(reading_numbers(0..).into_error(), Error::InvalidItem(0));

Implementations

impl Void

pub fn to<T>(self) -> T

Converts a Void to any type.

Note that because Void is impossible to construct, this method is unreachable.

Trait Implementations

impl Clone for Void

fn clone(&self) -> Void

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Void

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for Void

This impl is only enabled if the “serde_” feature is enabled.

This always Returns an Err(D::Error::custom(DeserializeVoidError)).

fn deserialize<D>(_: D) -> Result<Self, D::Error>

where D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Display for Void

fn fmt(&self, _: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Error for Void

fn description(&self) -> &str

👎Deprecated since 1.42.0: use the Display impl or to_string()

fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any.

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0: replaced by Error::source, which can support downcasting

fn provide<'a>(&'a self, request: &mut Request<'a>)

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

Provides type-based access to context intended for error reports.

impl From<Infallible> for Void

There’s also a impl From<Void> for std_::convert::Infallible impl that’s not appearing in the docs for some reason.

fn from(this: Infallible) -> Self

Converts to this type from the input type.

impl From<Void> for Infallible

fn from(this: Void) -> Self

Converts to this type from the input type.

impl Hash for Void

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for Void

fn cmp(&self, _: &Self) -> Ordering

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl<T: ?Sized> PartialEq<T> for Void

fn eq(&self, _: &T) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<T: ?Sized> PartialOrd<T> for Void

fn partial_cmp(&self, _: &T) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Rhs) -> bool

Tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Rhs) -> bool

Tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Rhs) -> bool

Tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Rhs) -> bool

Tests greater than or equal to (for self and other) and is used by the >= operator.

impl Serialize for Void

This impl is only enabled if the “serde_” feature is enabled.

fn serialize<S>(&self, _: S) -> Result<S::Ok, S::Error>

where S: Serializer,

Serialize this value into the given Serde serializer.

impl Copy for Void

impl Eq for Void