Enum wasmer_wasix::syscalls::Infallible

pub(crate) enum Infallible {}

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.

Trait Implementations

impl Clone for Infallible

fn clone(&self) -> Infallible

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T> Context<T, Infallible> for Option<T>

use anyhow::{Context, Result};

fn maybe_get() -> Option<T> {
    ...
}

fn demo() -> Result<()> {
    let t = maybe_get().context("there is no T")?;
    ...
}

fn context<C>(self, context: C) -> Result<T, Error>

where C: Display + Send + Sync + 'static,

Wrap the error value with additional context.

fn with_context<C, F>(self, context: F) -> Result<T, Error>

where C: Display + Send + Sync + 'static, F: FnOnce() -> C,

Wrap the error value with additional context that is evaluated lazily only once an error does occur.

impl Debug for Infallible

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

Formats the value using the given formatter.

impl Display for Infallible

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

Formats the value using the given formatter.

impl Error for Infallible

fn description(&self) -> &str

👎Deprecated since 1.42.0: use the Display impl or to_string()

fn source(&self) -> Option<&(dyn Error + 'static)>

The lower-level source of this error, if any.

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0: replaced by Error::source, which can support downcasting

fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (error_generic_member_access)

Provides type based access to context intended for error reports.

impl From<!> for Infallible

fn from(x: !) -> Infallible

Converts to this type from the input type.

impl Hash for Infallible

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

where H: Hasher,

Feeds this value into the given Hasher.

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

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl Ord for Infallible

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

This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized + PartialOrd,

Restrict a value to a certain interval.

impl PartialEq for Infallible

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

This method tests for self and other values to be equal, and is used by ==.

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.

impl PartialOrd for Infallible

fn partial_cmp(&self, _other: &Infallible) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

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

This method tests less than (for self and other) and is used by the < operator.

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

This method tests less than or equal to (for self and other) and is used by the <= operator.

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

This method tests greater than (for self and other) and is used by the > operator.

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

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl Termination for Infallible

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.

impl Trace for Infallible

fn trace<R>(self, _: R) -> Infallible

where R: Debug + Display + Send + Sync + 'static,

Adds an additional trace to this error, returning a new error.

impl WasmTypeList for Infallible

type CStruct = Infallible

The C type (a struct) that can hold/represent all the represented values.

type Array = [RawValue; 0]

The array type that can hold all the represented values.

fn size() -> u32

The size of the array

unsafe fn from_array( _: &mut impl AsStoreMut, _: <Infallible as WasmTypeList>::Array, ) -> Infallible

Constructs Self based on an array of values.

unsafe fn from_slice( _: &mut impl AsStoreMut, _: &[RawValue], ) -> Result<Infallible, TryFromSliceError>

Constructs Self based on a slice of values.

unsafe fn into_array( self, _: &mut impl AsStoreMut, ) -> <Infallible as WasmTypeList>::Array

Builds and returns an array of type Array from a tuple (list) of values.

fn empty_array() -> <Infallible as WasmTypeList>::Array

Allocates and return an empty array of type Array that will hold a tuple (list) of values, usually to hold the returned values of a WebAssembly function call.

unsafe fn from_c_struct( _: &mut impl AsStoreMut, self_: <Infallible as WasmTypeList>::CStruct, ) -> Infallible

Builds a tuple (list) of values from a C struct of type CStruct.

unsafe fn into_c_struct( self, _: &mut impl AsStoreMut, ) -> <Infallible as WasmTypeList>::CStruct

Builds and returns a C struct of type CStruct from a tuple (list) of values.

unsafe fn write_c_struct_to_ptr( _: <Infallible as WasmTypeList>::CStruct, _: *mut RawValue, )

Writes the contents of a C struct to an array of RawValue.

fn wasm_types() -> &'static [Type]

Get the Wasm types for the tuple (list) of currently represented values.

impl Copy for Infallible

impl Eq for Infallible

impl Never for Infallible

impl RmpReadErr for Infallible

impl RmpWriteErr for Infallible