# 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.

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    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`
        }
    }

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## 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:

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    pub type Infallible = !;

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… 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 {}

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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§

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### impl Clone for Infallible

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#### fn clone(&self) -> Infallible

Returns a copy of the value. Read more
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#### 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
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### 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
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#### fn source(&self) -> Option<&(dyn Error + 'static)>

The lower-level source of this error, if any. Read more
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#### 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, 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
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### impl From<!> for Infallible

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

Converts to this type from the input type.
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### impl From<Infallible> for TryFromIntError

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

Converts to this type from the input type.
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### impl From<Infallible> for TryFromSliceError

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

Converts to this type from the input type.
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### 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
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#### fn hash_slice<H>(data: &[Self], state: &mut H)where H: Hasher, Self: Sized,

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

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

Compares and returns the minimum of two values. Read more
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#### fn clamp(self, min: Self, max: Self) -> Selfwhere Self: Sized + PartialOrd,

Restrict a value to a certain interval. Read more
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### impl PartialEq 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 `==`.
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#### 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.
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### impl PartialOrd 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
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#### fn lt(&self, other: &Rhs) -> bool

This method tests less than (for `self` and `other`) and is used by the `<` operator. Read more
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#### 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
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#### fn gt(&self, other: &Rhs) -> bool

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

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### impl Eq for Infallible

## Auto Trait Implementations§

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### impl RefUnwindSafe for Infallible

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### impl Send for Infallible

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### impl Sync for Infallible

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### impl Unpin for Infallible

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### impl UnwindSafe for Infallible

## Blanket Implementations§

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

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

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for Twhere T: ?Sized,

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

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for Twhere T: ?Sized,

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

Mutably borrows from an owned value. Read more
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### impl<T> From<!> for T

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

Converts to this type from the input type.
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### impl<T> From<T> for T

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

Returns the argument unchanged.

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

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

Calls `U::from(self)`.

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

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### impl<T> ToOwned for Twhere T: Clone,

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#### type Owned = T

The resulting type after obtaining ownership.
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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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#### fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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### impl<T> ToString for Twhere T: Display + ?Sized,

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#### default fn to_string(&self) -> String

Converts the given value to a `String`. Read more
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### impl<T, U> TryFrom<U> for Twhere U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for Twhere U: TryFrom<T>,

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

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.