Enum std::convert::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.

i

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:

i

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 to have 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

const: unstable · source

impl Clone for Infallible

const: unstable · source

fn clone(&self) -> Infallible

Returns a copy of the value. Read more

1.0.0 · source

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

Performs copy-assignment from source. Read more

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impl Debug for Infallible

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

Formats the value using the given formatter. Read more

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impl Display for Infallible

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

Formats the value using the given formatter. Read more

1.8.0 · source

impl Error for Infallible

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fn description(&self) -> &str

👎 Deprecated since 1.42.0:

use the Display impl or to_string()

Read more

1.30.0 · source

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

The lower-level source of this error, if any. Read more

1.0.0 · source

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

👎 Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

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fn provide<'a>(&'a self, req: &mut Demand<'a>)

🔬 This is a nightly-only experimental API. (error_generic_member_access #99301)

Provides type based access to context intended for error reports. Read more

const: unstable · source

impl From<!> for Infallible

const: unstable · source

fn from(x: !) -> Infallible

Converts to this type from the input type.

const: unstable · source

impl From<Infallible> for TryFromIntError

const: unstable · source

fn from(x: Infallible) -> TryFromIntError

Converts to this type from the input type.

1.36.0 (const: unstable) · source

impl From<Infallible> for TryFromSliceError

const: unstable · source

fn from(x: Infallible) -> TryFromSliceError

Converts to this type from the input type.

1.44.0 · source

impl Hash for Infallible

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

Feeds this value into the given Hasher. Read more

1.3.0 · source

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

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

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impl Ord for Infallible

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

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

1.21.0 · source

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

Compares and returns the maximum of two values. Read more

1.21.0 · source

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

Compares and returns the minimum of two values. Read more

1.50.0 · source

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

Restrict a value to a certain interval. Read more

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impl PartialEq<Infallible> for Infallible

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

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

1.0.0 · source

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

This method tests for !=.

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impl PartialOrd<Infallible> for Infallible

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

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

1.0.0 · source

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

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

1.0.0 · source

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

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

1.0.0 · source

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

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

1.0.0 · source

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

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

1.61.0 · source

impl Termination for Infallible

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fn report(self) -> ExitCode

Is called to get the representation of the value as status code. This status code is returned to the operating system. Read more

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impl Copy for Infallible

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impl Eq for Infallible