Infallible in core::convert - Rust (original) (raw)
Enum 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`
}
}§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 = !;… 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 {}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.
👎Deprecated since 1.42.0: use the Display impl or to_string()
Returns the lower-level source of this error, if any. Read more
👎Deprecated since 1.33.0: replaced by Error::source, which can support downcasting
🔬This is a nightly-only experimental API. (error_generic_member_access #99301)
Provides type-based access to context intended for error reports. Read more
Converts to this type from the input type.
Converts to this type from the input type.
Converts to this type from the input type.
Tests for self and other values to be equal, and is used by ==.
Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
This method returns an ordering between self and other values if one exists. Read more
Tests less than (for self and other) and is used by the < operator. Read more
Tests less than or equal to (for self and other) and is used by the<= operator. Read more
Tests greater than (for self and other) and is used by the >operator. Read more
Tests greater than or equal to (for self and other) and is used by the >= operator. Read more