# Enum core::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.

ⓘ

    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 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 `impl`s will start to overlap and therefore will be disallowed by the language’s trait coherence rules.

## Trait Implementations§

source§

### impl Clone for Infallible

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
source§

### impl Debug for Infallible

source§

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

Formats the value using the given formatter. Read more
source§

### impl Display for Infallible

source§

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

Formats the value using the given formatter. Read more
1.8.0 · source§

### impl Error for Infallible

source§

#### 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
source§

#### fn provide<'a>(&'a self, request: &mut Request<'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
source§

### impl From<!> for Infallible

source§

#### fn from(x: !) -> Self

Converts to this type from the input type.
source§

### impl From<Infallible> for TryFromIntError

source§

#### fn from(x: Infallible) -> TryFromIntError

Converts to this type from the input type.
1.36.0 · source§

### impl From<Infallible> for TryFromSliceError

source§

#### fn from(x: Infallible) -> TryFromSliceError

Converts to this type from the input type.
1.44.0 · source§

### impl Hash for Infallible

source§

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

Feeds this value into the given `Hasher`. Read more
1.3.0 · source§

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

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

### impl Ord for Infallible

source§

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

This method returns an `Ordering` between `self` and `other`. Read more
1.21.0 · source§

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

Compares and returns the maximum of two values. Read more
1.21.0 · source§

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

Compares and returns the minimum of two values. Read more
1.50.0 · source§

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

Restrict a value to a certain interval. Read more
source§

### impl PartialEq for Infallible

source§

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

This method tests for `self` and `other` values to be equal, and is used by `==`.
1.0.0 · source§

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

This method tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
source§

### impl PartialOrd for Infallible

source§

#### fn partial_cmp(&self, _other: &Self) -> 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
source§

### impl Copy for Infallible

source§

### 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§

source§

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

source§

#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
source§

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

source§

#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
source§

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

source§

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

Mutably borrows from an owned value. Read more
source§

### impl<T> From<!> for T

source§

#### fn from(t: !) -> T

Converts to this type from the input type.
source§

### impl<T> From<T> for T

source§

#### fn from(t: T) -> T

Returns the argument unchanged.

source§

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

source§

#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

source§

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

§

#### type Error = Infallible

The type returned in the event of a conversion error.
source§

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

Performs the conversion.
source§

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

§

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

The type returned in the event of a conversion error.
source§

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

Performs the conversion.