Enum Infallible

1.34.0 · Source

pub enum Infallible {}

Expand description

The error type for errors that can never happen.

Since this enum has no variant, a value of this type can never actually exist. This can be useful for generic APIs that use Result and parameterize the error type, to indicate that the result is always Ok.

For example, the TryFrom trait (conversion that returns a Result) has a blanket implementation for all types where a reverse Into implementation exists.

impl<T, U> TryFrom<U> for T where U: Into<T> {
    type Error = Infallible;

    fn try_from(value: U) -> Result<Self, Infallible> {
        Ok(U::into(value))  // Never returns `Err`
    }
}

§Future compatibility

This enum has the same role as the ! “never” type, which is unstable in this version of Rust. When ! is stabilized, we plan to make Infallible a type alias to it:

pub type Infallible = !;

… and eventually deprecate Infallible.

However there is one case where ! syntax can be used before ! is stabilized as a full-fledged type: in the position of a function’s return type. Specifically, it is possible to have implementations for two different function pointer types:

trait MyTrait {}
impl MyTrait for fn() -> ! {}
impl MyTrait for fn() -> std::convert::Infallible {}

With Infallible being an enum, this code is valid. However when Infallible becomes an alias for the never type, the two impls will start to overlap and therefore will be disallowed by the language’s trait coherence rules.

Trait Implementations§

1.34.0 · Source§

Enum InfallibleCopy item path

§Future compatibility

Trait Implementations§

impl Clone for Infallible

fn clone(&self) -> Infallible

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

impl<T> Context<T, Infallible> for Option<T>

fn context<C>(self, context: C) -> Result<T, Error>where C: Display + Send + Sync + 'static,

fn with_context<C, F>(self, context: F) -> Result<T, Error>where C: Display + Send + Sync + 'static, F: FnOnce() -> C,

impl Debug for Infallible

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

impl Display for Infallible

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

impl Error for Infallible

fn description(&self) -> &str

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

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

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

impl From<!> for Infallible

fn from(x: !) -> Infallible

impl<Src, Dst> From<AlignmentError<Src, Dst>> for Infalliblewhere Dst: Unaligned + ?Sized,

fn from(_: AlignmentError<Src, Dst>) -> Infallible

impl From<Infallible> for Error

fn from(err: Infallible) -> Error

impl From<Infallible> for TryFromIntError

fn from(x: Infallible) -> TryFromIntError

impl From<Infallible> for TryFromSliceError

fn from(x: Infallible) -> TryFromSliceError

impl Hash for Infallible

fn hash<H>(&self, _: &mut H)where H: Hasher,

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

impl IntoResponse for Infallible

fn into_response(self) -> Response<Body>

impl Ord for Infallible

fn cmp(&self, _other: &Infallible) -> Ordering

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

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

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

impl PartialEq for Infallible

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

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

impl PartialOrd for Infallible

fn partial_cmp(&self, _other: &Infallible) -> Option<Ordering>

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

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

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

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

impl Termination for Infallible

fn report(self) -> ExitCode

impl Copy for Infallible

impl Eq for Infallible

Auto Trait Implementations§

impl Freeze for Infallible

impl RefUnwindSafe for Infallible

impl Send for Infallible

impl Sync for Infallible

impl Unpin for Infallible

impl UnwindSafe for Infallible

Blanket Implementations§

impl<T> Any for Twhere T: 'static + ?Sized,

fn type_id(&self) -> TypeId

impl<T> Borrow<T> for Twhere T: ?Sized,

fn borrow(&self) -> &T

impl<T> BorrowMut<T> for Twhere T: ?Sized,

fn borrow_mut(&mut self) -> &mut T

impl<T> CloneToUninit for Twhere T: Clone,

unsafe fn clone_to_uninit(&self, dst: *mut u8)

impl<Q, K> Comparable<K> for Qwhere Q: Ord + ?Sized, K: Borrow<Q> + ?Sized,

fn compare(&self, key: &K) -> Ordering

impl<Q, K> Equivalent<K> for Qwhere Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

fn equivalent(&self, key: &K) -> bool

impl<Q, K> Equivalent<K> for Qwhere Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

fn equivalent(&self, key: &K) -> bool

impl<T> From<!> for T

fn from(t: !) -> T

impl<T> From<T> for T

fn from(t: T) -> T

impl<T> FromRef<T> for Twhere T: Clone,

fn from_ref(input: &T) -> T

impl<T, S> Handler<IntoResponseHandler, S> for Twhere T: IntoResponse + Clone + Send + Sync + 'static,

Enum Infallible

fn context<C>(self, context: C) -> Result<T, Error>
where C: Display + Send + Sync + 'static,

fn with_context<C, F>(self, context: F) -> Result<T, Error>
where C: Display + Send + Sync + 'static, F: FnOnce() -> C,

impl<Src, Dst> From<AlignmentError<Src, Dst>> for Infallible
where Dst: Unaligned + ?Sized,

fn hash<H>(&self, _: &mut H)
where H: Hasher,

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

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

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

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

impl<T> Any for T
where T: 'static + ?Sized,

impl<T> Borrow<T> for T
where T: ?Sized,

impl<T> BorrowMut<T> for T
where T: ?Sized,

impl<T> CloneToUninit for T
where T: Clone,

impl<Q, K> Comparable<K> for Q
where Q: Ord + ?Sized, K: Borrow<Q> + ?Sized,

impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

impl<T> FromRef<T> for T
where T: Clone,

impl<T, S> Handler<IntoResponseHandler, S> for T
where T: IntoResponse + Clone + Send + Sync + 'static,

fn layer<L>(self, layer: L) -> Layered<L, Self, T, S>
where L: Layer<HandlerService<Self, T, S>> + Clone, <L as Layer<HandlerService<Self, T, S>>>::Service: Service<Request<Body>>,

impl<H, T> HandlerWithoutStateExt<T> for H
where H: Handler<T, ()>,

impl<T, U> Into<U> for T
where U: From<T>,

fn into_either_with<F>(self, into_left: F) -> Either<Self, Self> ⓘ
where F: FnOnce(&Self) -> bool,

impl<T> QuickClone<T> for T
where T: Clone,

impl<T> QuickToOwned for T
where T: ToOwned,

impl<T> QuickToString for T
where T: ToString + ?Sized,

impl<T> ToOwned for T
where T: Clone,

impl<T> ToString for T
where T: Display + ?Sized,

impl<T, U> TryFrom<U> for T
where U: Into<T>,

impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

impl<V, T> VZip<V> for T
where V: MultiLane<T>,

fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self> ⓘ
where S: Into<Dispatch>,

impl<T> ErasedDestructor for T
where T: 'static,

impl<T> RuleType for T
where T: Copy + Debug + Eq + Hash + Ord,