Enum std::convert::Infallible

pub enum Infallible {}

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.

ⓘ This example is not tested

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:

ⓘ This example is not tested

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 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.

Enum std::convert::Infallible

Future compatibility

Trait Implementations

impl Clone for Infallible

pub fn clone(&self) -> Infallible

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

impl Debug for Infallible

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

impl Display for Infallible

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

impl Error for Infallible

fn description(&self) -> &str

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

fn backtrace(&self) -> Option<&Backtrace>

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

impl From<!> for Infallible

pub fn from(x: !) -> Infallible

impl From<Infallible> for TryFromSliceError

pub fn from(x: Infallible) -> TryFromSliceError

impl From<Infallible> for TryFromIntError

pub fn from(x: Infallible) -> TryFromIntError

impl Hash for Infallible

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

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

impl Ord for Infallible

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

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

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

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

impl PartialEq<Infallible> for Infallible

pub fn eq(&self, &Infallible) -> bool

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

impl PartialOrd<Infallible> for Infallible

pub 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 Copy for Infallible

impl Eq for Infallible

Auto Trait Implementations

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 T where T: 'static + ?Sized,

pub fn type_id(&self) -> TypeId

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

pub fn borrow(&self) -> &T

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

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

impl<T> From<!> for T

pub fn from(t: !) -> T

impl<T> From<T> for T

pub fn from(t: T) -> T

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

pub fn into(self) -> U

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

type Owned = T

pub fn to_owned(&self) -> T

pub fn clone_into(&self, target: &mut T)

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

pub default fn to_string(&self) -> String

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

type Error = Infallible

pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

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

type Error = <U as TryFrom<T>>::Error

pub fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

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

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

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

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>,