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.
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`
}
}
RunFuture 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 {}
RunWith 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
const: unstable · sourceimpl Clone for Infallible
impl Clone for Infallible
const: unstable · sourcefn clone(&self) -> Infallible
fn clone(&self) -> Infallible
Returns a copy of the value. Read more
1.0.0 · sourcefn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
Performs copy-assignment from source
. Read more
sourceimpl Debug for Infallible
impl Debug for Infallible
sourceimpl Display for Infallible
impl Display for Infallible
1.8.0 · sourceimpl Error for Infallible
impl Error for Infallible
sourcefn description(&self) -> &str
fn description(&self) -> &str
use the Display impl or to_string()
1.30.0 · sourcefn source(&self) -> Option<&(dyn Error + 'static)>
fn source(&self) -> Option<&(dyn Error + 'static)>
The lower-level source of this error, if any. Read more
const: unstable · sourceimpl From<!> for Infallible
impl From<!> for Infallible
const: unstable · sourcefn from(x: !) -> Infallible
fn from(x: !) -> Infallible
Converts to this type from the input type.
1.36.0 (const: unstable) · sourceimpl From<Infallible> for TryFromSliceError
impl From<Infallible> for TryFromSliceError
const: unstable · sourcefn from(x: Infallible) -> TryFromSliceError
fn from(x: Infallible) -> TryFromSliceError
Converts to this type from the input type.
const: unstable · sourceimpl From<Infallible> for TryFromIntError
impl From<Infallible> for TryFromIntError
const: unstable · sourcefn from(x: Infallible) -> TryFromIntError
fn from(x: Infallible) -> TryFromIntError
Converts to this type from the input type.
1.44.0 · sourceimpl Hash for Infallible
impl Hash for Infallible
sourceimpl Ord for Infallible
impl Ord for Infallible
sourceimpl PartialEq<Infallible> for Infallible
impl PartialEq<Infallible> for Infallible
sourceimpl PartialOrd<Infallible> for Infallible
impl PartialOrd<Infallible> for Infallible
sourcefn partial_cmp(&self, _other: &Infallible) -> Option<Ordering>
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 · sourcefn lt(&self, other: &Rhs) -> bool
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 · sourcefn le(&self, other: &Rhs) -> bool
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
1.61.0 · sourceimpl Termination for Infallible
impl Termination for Infallible
impl Copy for Infallible
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
sourceimpl<T> BorrowMut<T> for T where
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more