Enum core::convert::Infallible1.34.0[][src]

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.

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`
    }
}
Run

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 = !;
Run

… 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 {}
Run

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

impl Clone for Infallible[src]

fn clone(&self) -> Infallible[src]

Returns a copy of the value. Read more

fn clone_from(&mut self, source: &Self)1.0.0[src]

Performs copy-assignment from source. Read more

impl Debug for Infallible[src]

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

Formats the value using the given formatter. Read more

impl Display for Infallible[src]

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

Formats the value using the given formatter. Read more

impl From<!> for Infallible[src]

fn from(x: !) -> Self[src]

Performs the conversion.

impl From<Infallible> for TryFromIntError[src]

fn from(x: Infallible) -> TryFromIntError[src]

Performs the conversion.

impl From<Infallible> for TryFromSliceError1.36.0[src]

fn from(x: Infallible) -> TryFromSliceError[src]

Performs the conversion.

impl Hash for Infallible1.44.0[src]

fn hash<H: Hasher>(&self, _: &mut H)[src]

Feeds this value into the given Hasher. Read more

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

Feeds a slice of this type into the given Hasher. Read more

impl Ord for Infallible[src]

fn cmp(&self, _other: &Self) -> Ordering[src]

This method returns an Ordering between self and other. Read more

#[must_use]
fn max(self, other: Self) -> Self where
    Self: Sized
1.21.0[src]

Compares and returns the maximum of two values. Read more

#[must_use]
fn min(self, other: Self) -> Self where
    Self: Sized
1.21.0[src]

Compares and returns the minimum of two values. Read more

#[must_use]
fn clamp(self, min: Self, max: Self) -> Self where
    Self: Sized
1.50.0[src]

Restrict a value to a certain interval. Read more

impl PartialEq<Infallible> for Infallible[src]

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

This method tests for self and other values to be equal, and is used by ==. Read more

#[must_use]
fn ne(&self, other: &Rhs) -> bool
1.0.0[src]

This method tests for !=.

impl PartialOrd<Infallible> for Infallible[src]

fn partial_cmp(&self, _other: &Self) -> Option<Ordering>[src]

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

#[must_use]
fn lt(&self, other: &Rhs) -> bool
1.0.0[src]

This method tests less than (for self and other) and is used by the < operator. Read more

#[must_use]
fn le(&self, other: &Rhs) -> bool
1.0.0[src]

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more

#[must_use]
fn gt(&self, other: &Rhs) -> bool
1.0.0[src]

This method tests greater than (for self and other) and is used by the > operator. Read more

#[must_use]
fn ge(&self, other: &Rhs) -> bool
1.0.0[src]

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more

impl Copy for Infallible[src]

impl Eq for Infallible[src]

Auto Trait Implementations

impl Send for Infallible

impl Sync for Infallible

impl Unpin for Infallible

Blanket Implementations

impl<T> Any for T where
    T: 'static + ?Sized
[src]

pub fn type_id(&Self) -> TypeId[src]

Gets the TypeId of self. Read more

impl<T> Borrow<T> for T where
    T: ?Sized
[src]

pub fn borrow(&Self) -> &T[src]

Immutably borrows from an owned value. Read more

impl<T> BorrowMut<T> for T where
    T: ?Sized
[src]

pub fn borrow_mut(&mut Self) -> &mut T[src]

Mutably borrows from an owned value. Read more

impl<T> From<!> for T[src]

pub fn from(!) -> T[src]

Performs the conversion.

impl<T> From<T> for T[src]

pub fn from(T) -> T[src]

Performs the conversion.

impl<T, U> Into<U> for T where
    U: From<T>, 
[src]

pub fn into(Self) -> U[src]

Performs the conversion.

impl<T, U> TryFrom<U> for T where
    U: Into<T>, 
[src]

type Error = Infallible

The type returned in the event of a conversion error.

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

Performs the conversion.

impl<T, U> TryInto<U> for T where
    U: TryFrom<T>, 
[src]

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

The type returned in the event of a conversion error.

pub fn try_into(Self) -> Result<U, <U as TryFrom<T>>::Error>[src]

Performs the conversion.