1.34.0[][src]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`
    }
}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:

This example is not tested
pub type Infallible = !;Run

… and eventually deprecate Infallible.

However there is one case where ! syntax can be used before ! is stabilized as a full-fleged 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 Display for Infallible[src]

impl Clone for Infallible[src]

fn clone_from(&mut self, source: &Self)
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Performs copy-assignment from source. Read more

impl PartialOrd<Infallible> for Infallible[src]

#[must_use]
fn lt(&self, other: &Rhs) -> bool
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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
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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
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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
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This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more

impl Ord for Infallible[src]

fn max(self, other: Self) -> Self
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Compares and returns the maximum of two values. Read more

fn min(self, other: Self) -> Self
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Compares and returns the minimum of two values. Read more

impl Eq for Infallible[src]

impl PartialEq<Infallible> for Infallible[src]

#[must_use]
fn ne(&self, other: &Rhs) -> bool
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This method tests for !=.

impl Debug for Infallible[src]

impl Copy for Infallible[src]

impl From<Infallible> for TryFromIntError[src]

impl From<!> for Infallible[src]

Auto Trait Implementations

impl Send for Infallible

impl Sync for Infallible

Blanket Implementations

impl<T> From for T[src]

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

type Error = Infallible

The type returned in the event of a conversion error.

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

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

The type returned in the event of a conversion error.

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

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

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

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

impl<T> ToOwned for T where
    T: Clone
[src]

type Owned = T

impl<T> ToString for T where
    T: Display + ?Sized
[src]