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`
}
}
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:
… 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 · source§impl Clone for Infallible
impl Clone for Infallible
source§impl Debug for Infallible
impl Debug for Infallible
source§impl Display for Infallible
impl Display for Infallible
1.8.0 · source§impl Error for Infallible
impl Error for Infallible
source§fn description(&self) -> &str
fn description(&self) -> &str
1.30.0 · source§fn source(&self) -> Option<&(dyn Error + 'static)>
fn source(&self) -> Option<&(dyn Error + 'static)>
const: unstable · source§impl From<Infallible> for TryFromIntError
impl From<Infallible> for TryFromIntError
const: unstable · source§fn from(x: Infallible) -> TryFromIntError
fn from(x: Infallible) -> TryFromIntError
1.36.0 (const: unstable) · source§impl From<Infallible> for TryFromSliceError
impl From<Infallible> for TryFromSliceError
const: unstable · source§fn from(x: Infallible) -> TryFromSliceError
fn from(x: Infallible) -> TryFromSliceError
1.44.0 · source§impl Hash for Infallible
impl Hash for Infallible
source§impl Ord for Infallible
impl Ord for Infallible
source§impl PartialEq<Infallible> for Infallible
impl PartialEq<Infallible> for Infallible
source§fn eq(&self, _: &Infallible) -> bool
fn eq(&self, _: &Infallible) -> bool
source§impl PartialOrd<Infallible> for Infallible
impl PartialOrd<Infallible> for Infallible
1.0.0 · source§fn le(&self, other: &Rhs) -> bool
fn le(&self, other: &Rhs) -> bool
self
and other
) and is used by the <=
operator. Read more