Enum frame_support::dispatch::result::Result

#[must_use = "this `Result` may be an `Err` variant, which should be handled"]pub enum Result<T, E> {
    Ok(T),
    Err(E),
}

Result is a type that represents either success (Ok) or failure (Err).

See the module documentation for details.

Variants

Ok(T)

Contains the success value

Err(E)

Contains the error value

Implementations

impl<T, E> Result<T, E>

#[must_use = "if you intended to assert that this is ok, consider `.unwrap()` instead"]pub const fn is_ok(&self) -> bool

Returns true if the result is Ok.

Examples

Basic usage:

let x: Result<i32, &str> = Ok(-3);
assert_eq!(x.is_ok(), true);

let x: Result<i32, &str> = Err("Some error message");
assert_eq!(x.is_ok(), false);

#[must_use = "if you intended to assert that this is err, consider `.unwrap_err()` instead"]pub const fn is_err(&self) -> bool

Returns true if the result is Err.

Examples

Basic usage:

let x: Result<i32, &str> = Ok(-3);
assert_eq!(x.is_err(), false);

let x: Result<i32, &str> = Err("Some error message");
assert_eq!(x.is_err(), true);

#[must_use]pub fn contains<U>(&self, x: &U) -> bool where
    U: PartialEq<T>, 

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

Returns true if the result is an Ok value containing the given value.

Examples

#![feature(option_result_contains)]

let x: Result<u32, &str> = Ok(2);
assert_eq!(x.contains(&2), true);

let x: Result<u32, &str> = Ok(3);
assert_eq!(x.contains(&2), false);

let x: Result<u32, &str> = Err("Some error message");
assert_eq!(x.contains(&2), false);

#[must_use]pub fn contains_err<F>(&self, f: &F) -> bool where
    F: PartialEq<E>, 

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

Returns true if the result is an Err value containing the given value.

Examples

#![feature(result_contains_err)]

let x: Result<u32, &str> = Ok(2);
assert_eq!(x.contains_err(&"Some error message"), false);

let x: Result<u32, &str> = Err("Some error message");
assert_eq!(x.contains_err(&"Some error message"), true);

let x: Result<u32, &str> = Err("Some other error message");
assert_eq!(x.contains_err(&"Some error message"), false);

pub fn ok(self) -> Option<T>

Converts from Result<T, E> to Option<T>.

Converts self into an Option<T>, consuming self, and discarding the error, if any.

Examples

Basic usage:

let x: Result<u32, &str> = Ok(2);
assert_eq!(x.ok(), Some(2));

let x: Result<u32, &str> = Err("Nothing here");
assert_eq!(x.ok(), None);

pub fn err(self) -> Option<E>

Converts from Result<T, E> to Option<E>.

Converts self into an Option<E>, consuming self, and discarding the success value, if any.

Examples

Basic usage:

let x: Result<u32, &str> = Ok(2);
assert_eq!(x.err(), None);

let x: Result<u32, &str> = Err("Nothing here");
assert_eq!(x.err(), Some("Nothing here"));

pub const fn as_ref(&self) -> Result<&T, &E>

Converts from &Result<T, E> to Result<&T, &E>.

Produces a new Result, containing a reference into the original, leaving the original in place.

Examples

Basic usage:

let x: Result<u32, &str> = Ok(2);
assert_eq!(x.as_ref(), Ok(&2));

let x: Result<u32, &str> = Err("Error");
assert_eq!(x.as_ref(), Err(&"Error"));

pub fn as_mut(&mut self) -> Result<&mut T, &mut E>

Converts from &mut Result<T, E> to Result<&mut T, &mut E>.

Examples

Basic usage:

fn mutate(r: &mut Result<i32, i32>) {
    match r.as_mut() {
        Ok(v) => *v = 42,
        Err(e) => *e = 0,
    }
}

let mut x: Result<i32, i32> = Ok(2);
mutate(&mut x);
assert_eq!(x.unwrap(), 42);

let mut x: Result<i32, i32> = Err(13);
mutate(&mut x);
assert_eq!(x.unwrap_err(), 0);

pub fn map<U, F>(self, op: F) -> Result<U, E> where
    F: FnOnce(T) -> U, 

Maps a Result<T, E> to Result<U, E> by applying a function to a contained Ok value, leaving an Err value untouched.

This function can be used to compose the results of two functions.

Examples

Print the numbers on each line of a string multiplied by two.

let line = "1\n2\n3\n4\n";

for num in line.lines() {
    match num.parse::<i32>().map(|i| i * 2) {
        Ok(n) => println!("{}", n),
        Err(..) => {}
    }
}

pub fn map_or<U, F>(self, default: U, f: F) -> U where
    F: FnOnce(T) -> U, 

Applies a function to the contained value (if Ok), or returns the provided default (if Err).

Arguments passed to map_or are eagerly evaluated; if you are passing the result of a function call, it is recommended to use map_or_else, which is lazily evaluated.

Examples

let x: Result<_, &str> = Ok("foo");
assert_eq!(x.map_or(42, |v| v.len()), 3);

let x: Result<&str, _> = Err("bar");
assert_eq!(x.map_or(42, |v| v.len()), 42);

pub fn map_or_else<U, D, F>(self, default: D, f: F) -> U where
    F: FnOnce(T) -> U,
    D: FnOnce(E) -> U, 

Maps a Result<T, E> to U by applying a function to a contained Ok value, or a fallback function to a contained Err value.

This function can be used to unpack a successful result while handling an error.

Examples

Basic usage:

let k = 21;

let x : Result<_, &str> = Ok("foo");
assert_eq!(x.map_or_else(|e| k * 2, |v| v.len()), 3);

let x : Result<&str, _> = Err("bar");
assert_eq!(x.map_or_else(|e| k * 2, |v| v.len()), 42);

pub fn map_err<F, O>(self, op: O) -> Result<T, F> where
    O: FnOnce(E) -> F, 

Maps a Result<T, E> to Result<T, F> by applying a function to a contained Err value, leaving an Ok value untouched.

This function can be used to pass through a successful result while handling an error.

Examples

Basic usage:

fn stringify(x: u32) -> String { format!("error code: {}", x) }

let x: Result<u32, u32> = Ok(2);
assert_eq!(x.map_err(stringify), Ok(2));

let x: Result<u32, u32> = Err(13);
assert_eq!(x.map_err(stringify), Err("error code: 13".to_string()));

pub fn iter(&self) -> Iter<'_, T>

Returns an iterator over the possibly contained value.

The iterator yields one value if the result is Result::Ok, otherwise none.

Examples

Basic usage:

let x: Result<u32, &str> = Ok(7);
assert_eq!(x.iter().next(), Some(&7));

let x: Result<u32, &str> = Err("nothing!");
assert_eq!(x.iter().next(), None);

pub fn iter_mut(&mut self) -> IterMut<'_, T>

Returns a mutable iterator over the possibly contained value.

The iterator yields one value if the result is Result::Ok, otherwise none.

Examples

Basic usage:

let mut x: Result<u32, &str> = Ok(7);
match x.iter_mut().next() {
    Some(v) => *v = 40,
    None => {},
}
assert_eq!(x, Ok(40));

let mut x: Result<u32, &str> = Err("nothing!");
assert_eq!(x.iter_mut().next(), None);

pub fn and<U>(self, res: Result<U, E>) -> Result<U, E>

Returns res if the result is Ok, otherwise returns the Err value of self.

Examples

Basic usage:

let x: Result<u32, &str> = Ok(2);
let y: Result<&str, &str> = Err("late error");
assert_eq!(x.and(y), Err("late error"));

let x: Result<u32, &str> = Err("early error");
let y: Result<&str, &str> = Ok("foo");
assert_eq!(x.and(y), Err("early error"));

let x: Result<u32, &str> = Err("not a 2");
let y: Result<&str, &str> = Err("late error");
assert_eq!(x.and(y), Err("not a 2"));

let x: Result<u32, &str> = Ok(2);
let y: Result<&str, &str> = Ok("different result type");
assert_eq!(x.and(y), Ok("different result type"));

pub fn and_then<U, F>(self, op: F) -> Result<U, E> where
    F: FnOnce(T) -> Result<U, E>, 

Calls op if the result is Ok, otherwise returns the Err value of self.

This function can be used for control flow based on Result values.

Examples

Basic usage:

fn sq(x: u32) -> Result<u32, u32> { Ok(x * x) }
fn err(x: u32) -> Result<u32, u32> { Err(x) }

assert_eq!(Ok(2).and_then(sq).and_then(sq), Ok(16));
assert_eq!(Ok(2).and_then(sq).and_then(err), Err(4));
assert_eq!(Ok(2).and_then(err).and_then(sq), Err(2));
assert_eq!(Err(3).and_then(sq).and_then(sq), Err(3));

pub fn or<F>(self, res: Result<T, F>) -> Result<T, F>

Returns res if the result is Err, otherwise returns the Ok value of self.

Arguments passed to or are eagerly evaluated; if you are passing the result of a function call, it is recommended to use or_else, which is lazily evaluated.

Examples

Basic usage:

let x: Result<u32, &str> = Ok(2);
let y: Result<u32, &str> = Err("late error");
assert_eq!(x.or(y), Ok(2));

let x: Result<u32, &str> = Err("early error");
let y: Result<u32, &str> = Ok(2);
assert_eq!(x.or(y), Ok(2));

let x: Result<u32, &str> = Err("not a 2");
let y: Result<u32, &str> = Err("late error");
assert_eq!(x.or(y), Err("late error"));

let x: Result<u32, &str> = Ok(2);
let y: Result<u32, &str> = Ok(100);
assert_eq!(x.or(y), Ok(2));

pub fn or_else<F, O>(self, op: O) -> Result<T, F> where
    O: FnOnce(E) -> Result<T, F>, 

Calls op if the result is Err, otherwise returns the Ok value of self.

This function can be used for control flow based on result values.

Examples

Basic usage:

fn sq(x: u32) -> Result<u32, u32> { Ok(x * x) }
fn err(x: u32) -> Result<u32, u32> { Err(x) }

assert_eq!(Ok(2).or_else(sq).or_else(sq), Ok(2));
assert_eq!(Ok(2).or_else(err).or_else(sq), Ok(2));
assert_eq!(Err(3).or_else(sq).or_else(err), Ok(9));
assert_eq!(Err(3).or_else(err).or_else(err), Err(3));

pub fn unwrap_or(self, default: T) -> T

Returns the contained Ok value or a provided default.

Arguments passed to unwrap_or are eagerly evaluated; if you are passing the result of a function call, it is recommended to use unwrap_or_else, which is lazily evaluated.

Examples

Basic usage:

let default = 2;
let x: Result<u32, &str> = Ok(9);
assert_eq!(x.unwrap_or(default), 9);

let x: Result<u32, &str> = Err("error");
assert_eq!(x.unwrap_or(default), default);

pub fn unwrap_or_else<F>(self, op: F) -> T where
    F: FnOnce(E) -> T, 

Returns the contained Ok value or computes it from a closure.

Examples

Basic usage:

fn count(x: &str) -> usize { x.len() }

assert_eq!(Ok(2).unwrap_or_else(count), 2);
assert_eq!(Err("foo").unwrap_or_else(count), 3);

pub unsafe fn unwrap_unchecked(self) -> T

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

newly added

Returns the contained Ok value, consuming the self value, without checking that the value is not an Err.

Safety

Calling this method on an Err is undefined behavior.

Examples

#![feature(option_result_unwrap_unchecked)]
let x: Result<u32, &str> = Ok(2);
assert_eq!(unsafe { x.unwrap_unchecked() }, 2);

#![feature(option_result_unwrap_unchecked)]
let x: Result<u32, &str> = Err("emergency failure");
unsafe { x.unwrap_unchecked(); } // Undefined behavior!

pub unsafe fn unwrap_err_unchecked(self) -> E

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

newly added

Returns the contained Err value, consuming the self value, without checking that the value is not an Ok.

Safety

Calling this method on an Ok is undefined behavior.

Examples

#![feature(option_result_unwrap_unchecked)]
let x: Result<u32, &str> = Ok(2);
unsafe { x.unwrap_err_unchecked() }; // Undefined behavior!

#![feature(option_result_unwrap_unchecked)]
let x: Result<u32, &str> = Err("emergency failure");
assert_eq!(unsafe { x.unwrap_err_unchecked() }, "emergency failure");

impl<'_, T, E> Result<&'_ T, E> where
    T: Copy, 

pub fn copied(self) -> Result<T, E>

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

newly added

Maps a Result<&T, E> to a Result<T, E> by copying the contents of the Ok part.

Examples

#![feature(result_copied)]
let val = 12;
let x: Result<&i32, i32> = Ok(&val);
assert_eq!(x, Ok(&12));
let copied = x.copied();
assert_eq!(copied, Ok(12));

impl<'_, T, E> Result<&'_ mut T, E> where
    T: Copy, 

pub fn copied(self) -> Result<T, E>

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

newly added

Maps a Result<&mut T, E> to a Result<T, E> by copying the contents of the Ok part.

Examples

#![feature(result_copied)]
let mut val = 12;
let x: Result<&mut i32, i32> = Ok(&mut val);
assert_eq!(x, Ok(&mut 12));
let copied = x.copied();
assert_eq!(copied, Ok(12));

impl<'_, T, E> Result<&'_ T, E> where
    T: Clone, 

pub fn cloned(self) -> Result<T, E>

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

newly added

Maps a Result<&T, E> to a Result<T, E> by cloning the contents of the Ok part.

Examples

#![feature(result_cloned)]
let val = 12;
let x: Result<&i32, i32> = Ok(&val);
assert_eq!(x, Ok(&12));
let cloned = x.cloned();
assert_eq!(cloned, Ok(12));

impl<'_, T, E> Result<&'_ mut T, E> where
    T: Clone, 

pub fn cloned(self) -> Result<T, E>

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

newly added

Maps a Result<&mut T, E> to a Result<T, E> by cloning the contents of the Ok part.

Examples

#![feature(result_cloned)]
let mut val = 12;
let x: Result<&mut i32, i32> = Ok(&mut val);
assert_eq!(x, Ok(&mut 12));
let cloned = x.cloned();
assert_eq!(cloned, Ok(12));

impl<T, E> Result<T, E> where
    E: Debug, 

pub fn expect(self, msg: &str) -> T

Returns the contained Ok value, consuming the self value.

Panics

Panics if the value is an Err, with a panic message including the passed message, and the content of the Err.

Examples

Basic usage:

let x: Result<u32, &str> = Err("emergency failure");
x.expect("Testing expect"); // panics with `Testing expect: emergency failure`

pub fn unwrap(self) -> T

Returns the contained Ok value, consuming the self value.

Because this function may panic, its use is generally discouraged. Instead, prefer to use pattern matching and handle the Err case explicitly, or call unwrap_or, unwrap_or_else, or unwrap_or_default.

Panics

Panics if the value is an Err, with a panic message provided by the Err’s value.

Examples

Basic usage:

let x: Result<u32, &str> = Ok(2);
assert_eq!(x.unwrap(), 2);

let x: Result<u32, &str> = Err("emergency failure");
x.unwrap(); // panics with `emergency failure`

impl<T, E> Result<T, E> where
    T: Debug, 

pub fn expect_err(self, msg: &str) -> E

Returns the contained Err value, consuming the self value.

Panics

Panics if the value is an Ok, with a panic message including the passed message, and the content of the Ok.

Examples

Basic usage:

let x: Result<u32, &str> = Ok(10);
x.expect_err("Testing expect_err"); // panics with `Testing expect_err: 10`

pub fn unwrap_err(self) -> E

Returns the contained Err value, consuming the self value.

Panics

Panics if the value is an Ok, with a custom panic message provided by the Ok’s value.

Examples

let x: Result<u32, &str> = Ok(2);
x.unwrap_err(); // panics with `2`

let x: Result<u32, &str> = Err("emergency failure");
assert_eq!(x.unwrap_err(), "emergency failure");

impl<T, E> Result<T, E> where
    T: Default, 

pub fn unwrap_or_default(self) -> T

Returns the contained Ok value or a default

Consumes the self argument then, if Ok, returns the contained value, otherwise if Err, returns the default value for that type.

Examples

Converts a string to an integer, turning poorly-formed strings into 0 (the default value for integers). parse converts a string to any other type that implements FromStr, returning an Err on error.

let good_year_from_input = "1909";
let bad_year_from_input = "190blarg";
let good_year = good_year_from_input.parse().unwrap_or_default();
let bad_year = bad_year_from_input.parse().unwrap_or_default();

assert_eq!(1909, good_year);
assert_eq!(0, bad_year);

impl<T, E> Result<T, E> where
    E: Into<!>, 

pub fn into_ok(self) -> T

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

newly added

Returns the contained Ok value, but never panics.

Unlike unwrap, this method is known to never panic on the result types it is implemented for. Therefore, it can be used instead of unwrap as a maintainability safeguard that will fail to compile if the error type of the Result is later changed to an error that can actually occur.

Examples

Basic usage:

fn only_good_news() -> Result<String, !> {
    Ok("this is fine".into())
}

let s: String = only_good_news().into_ok();
println!("{}", s);

impl<T, E> Result<T, E> where
    T: Deref, 

pub fn as_deref(&self) -> Result<&<T as Deref>::Target, &E>

Converts from Result<T, E> (or &Result<T, E>) to Result<&<T as Deref>::Target, &E>.

Coerces the Ok variant of the original Result via Deref and returns the new Result.

Examples

let x: Result<String, u32> = Ok("hello".to_string());
let y: Result<&str, &u32> = Ok("hello");
assert_eq!(x.as_deref(), y);

let x: Result<String, u32> = Err(42);
let y: Result<&str, &u32> = Err(&42);
assert_eq!(x.as_deref(), y);

impl<T, E> Result<T, E> where
    T: DerefMut, 

pub fn as_deref_mut(&mut self) -> Result<&mut <T as Deref>::Target, &mut E>

Converts from Result<T, E> (or &mut Result<T, E>) to Result<&mut <T as DerefMut>::Target, &mut E>.

Coerces the Ok variant of the original Result via DerefMut and returns the new Result.

Examples

let mut s = "HELLO".to_string();
let mut x: Result<String, u32> = Ok("hello".to_string());
let y: Result<&mut str, &mut u32> = Ok(&mut s);
assert_eq!(x.as_deref_mut().map(|x| { x.make_ascii_uppercase(); x }), y);

let mut i = 42;
let mut x: Result<String, u32> = Err(42);
let y: Result<&mut str, &mut u32> = Err(&mut i);
assert_eq!(x.as_deref_mut().map(|x| { x.make_ascii_uppercase(); x }), y);

impl<T, E> Result<Option<T>, E>

pub const fn transpose(self) -> Option<Result<T, E>>

Transposes a Result of an Option into an Option of a Result.

Ok(None) will be mapped to None. Ok(Some(_)) and Err(_) will be mapped to Some(Ok(_)) and Some(Err(_)).

Examples

#[derive(Debug, Eq, PartialEq)]
struct SomeErr;

let x: Result<Option<i32>, SomeErr> = Ok(Some(5));
let y: Option<Result<i32, SomeErr>> = Some(Ok(5));
assert_eq!(x.transpose(), y);

impl<T, E> Result<Result<T, E>, E>

pub fn flatten(self) -> Result<T, E>

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

Converts from Result<Result<T, E>, E> to Result<T, E>

Examples

Basic usage:

#![feature(result_flattening)]
let x: Result<Result<&'static str, u32>, u32> = Ok(Ok("hello"));
assert_eq!(Ok("hello"), x.flatten());

let x: Result<Result<&'static str, u32>, u32> = Ok(Err(6));
assert_eq!(Err(6), x.flatten());

let x: Result<Result<&'static str, u32>, u32> = Err(6);
assert_eq!(Err(6), x.flatten());

Flattening only removes one level of nesting at a time:

#![feature(result_flattening)]
let x: Result<Result<Result<&'static str, u32>, u32>, u32> = Ok(Ok(Ok("hello")));
assert_eq!(Ok(Ok("hello")), x.flatten());
assert_eq!(Ok("hello"), x.flatten().flatten());

impl<T> Result<T, T>

pub const fn into_ok_or_err(self) -> T

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

newly added

Returns the Ok value if self is Ok, and the Err value if self is Err.

In other words, this function returns the value (the T) of a Result<T, T>, regardless of whether or not that result is Ok or Err.

This can be useful in conjunction with APIs such as Atomic*::compare_exchange, or slice::binary_search, but only in cases where you don’t care if the result was Ok or not.

Examples

#![feature(result_into_ok_or_err)]
let ok: Result<u32, u32> = Ok(3);
let err: Result<u32, u32> = Err(4);

assert_eq!(ok.into_ok_or_err(), 3);
assert_eq!(err.into_ok_or_err(), 4);

Trait Implementations

impl<T, E> Clone for Result<T, E> where
    T: Clone,
    E: Clone, 

pub fn clone(&self) -> Result<T, E>

Returns a copy of the value.

pub fn clone_from(&mut self, source: &Result<T, E>)

Performs copy-assignment from source.

impl<T, E> Copy for Result<T, E> where
    T: Copy,
    E: Copy, 

impl<T, E> Debug for Result<T, E> where
    T: Debug,
    E: Debug, 

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

Formats the value using the given formatter.

impl<T, E> Decode for Result<T, E> where
    T: Decode,
    E: Decode, 

pub fn decode<I>(input: &mut I) -> Result<Result<T, E>, Error> where
    I: Input, 

Attempt to deserialise the value from input.

impl<'de, T, E> Deserialize<'de> for Result<T, E> where
    T: Deserialize<'de>,
    E: Deserialize<'de>, 

pub fn deserialize<D>(
    deserializer: D
) -> Result<Result<T, E>, <D as Deserializer<'de>>::Error> where
    D: Deserializer<'de>, 

Deserialize this value from the given Serde deserializer.

impl<T, E> Encode for Result<T, E> where
    T: Encode,
    E: Encode, 

pub fn size_hint(&self) -> usize

If possible give a hint of expected size of the encoding.

pub fn encode_to<W>(&self, dest: &mut W) where
    W: Output, 

Convert self to a slice and append it to the destination.

pub fn encode(&self) -> Vec<u8, Global>

Convert self to an owned vector.

pub fn using_encoded<R, F>(&self, f: F) -> R where
    F: FnOnce(&[u8]) -> R, 

Convert self to a slice and then invoke the given closure with it.

impl<T, LikeT, E, LikeE> EncodeLike<Result<LikeT, LikeE>> for Result<T, E> where
    T: EncodeLike<LikeT>,
    E: EncodeLike<LikeE>,
    LikeT: Encode,
    LikeE: Encode, 

impl<T, E> Eq for Result<T, E> where
    T: Eq,
    E: Eq, 

impl<'_> From<&'_ StreamResult> for Result<MZStatus, MZError>

pub fn from(res: &StreamResult) -> Result<MZStatus, MZError>

Performs the conversion.

impl<'_> From<&'_ StreamResult> for Result<MZStatus, MZError>

pub fn from(res: &StreamResult) -> Result<MZStatus, MZError>

Performs the conversion.

impl From<DispatchError> for Result<(), DispatchError>

pub fn from(err: DispatchError) -> Result<(), DispatchError>

Performs the conversion.

impl From<StreamResult> for Result<MZStatus, MZError>

pub fn from(res: StreamResult) -> Result<MZStatus, MZError>

Performs the conversion.

impl From<StreamResult> for Result<MZStatus, MZError>

pub fn from(res: StreamResult) -> Result<MZStatus, MZError>

Performs the conversion.

impl From<ValidTransactionBuilder> for Result<ValidTransaction, TransactionValidityError>

pub fn from(
    builder: ValidTransactionBuilder
) -> Result<ValidTransaction, TransactionValidityError>

Performs the conversion.

impl<A, E, V> FromIterator<Result<A, E>> for Result<V, E> where
    V: FromIterator<A>, 

pub fn from_iter<I>(iter: I) -> Result<V, E> where
    I: IntoIterator<Item = Result<A, E>>, 

Takes each element in the Iterator: if it is an Err, no further elements are taken, and the Err is returned. Should no Err occur, a container with the values of each Result is returned.

Here is an example which increments every integer in a vector, checking for overflow:

let v = vec![1, 2];
let res: Result<Vec<u32>, &'static str> = v.iter().map(|x: &u32|
    x.checked_add(1).ok_or("Overflow!")
).collect();
assert_eq!(res, Ok(vec![2, 3]));

Here is another example that tries to subtract one from another list of integers, this time checking for underflow:

let v = vec![1, 2, 0];
let res: Result<Vec<u32>, &'static str> = v.iter().map(|x: &u32|
    x.checked_sub(1).ok_or("Underflow!")
).collect();
assert_eq!(res, Err("Underflow!"));

Here is a variation on the previous example, showing that no further elements are taken from iter after the first Err.

let v = vec![3, 2, 1, 10];
let mut shared = 0;
let res: Result<Vec<u32>, &'static str> = v.iter().map(|x: &u32| {
    shared += x;
    x.checked_sub(2).ok_or("Underflow!")
}).collect();
assert_eq!(res, Err("Underflow!"));
assert_eq!(shared, 6);

Since the third element caused an underflow, no further elements were taken, so the final value of shared is 6 (= 3 + 2 + 1), not 16.

impl<C, T, E> FromParallelIterator<Result<T, E>> for Result<C, E> where
    C: FromParallelIterator<T>,
    T: Send,
    E: Send, 

Collect an arbitrary Result-wrapped collection.

If any item is Err, then all previous Ok items collected are discarded, and it returns that error. If there are multiple errors, the one returned is not deterministic.

pub fn from_par_iter<I>(par_iter: I) -> Result<C, E> where
    I: IntoParallelIterator<Item = Result<T, E>>, 

Creates an instance of the collection from the parallel iterator par_iter.

impl<T, E> Hash for Result<T, E> where
    T: Hash,
    E: Hash, 

pub fn hash<__H>(&self, state: &mut __H) where
    __H: Hasher, 

Feeds this value into the given Hasher.

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

Feeds a slice of this type into the given Hasher.

impl<T, E> IntoFuture for Result<T, E>

type Future = FutureResult<T, E>

The future that this type can be converted into.

type Item = T

The item that the future may resolve with.

type Error = E

The error that the future may resolve with.

pub fn into_future(self) -> FutureResult<T, E>

Consumes this object and produces a future.

impl<'a, T, E> IntoIterator for &'a mut Result<T, E>

type Item = &'a mut T

The type of the elements being iterated over.

type IntoIter = IterMut<'a, T>

Which kind of iterator are we turning this into?

pub fn into_iter(self) -> IterMut<'a, T>

Creates an iterator from a value.

impl<T, E> IntoIterator for Result<T, E>

type Item = T

The type of the elements being iterated over.

type IntoIter = IntoIter<T>

Which kind of iterator are we turning this into?

pub fn into_iter(self) -> IntoIter<T>

Returns a consuming iterator over the possibly contained value.

The iterator yields one value if the result is Result::Ok, otherwise none.

Examples

Basic usage:

let x: Result<u32, &str> = Ok(5);
let v: Vec<u32> = x.into_iter().collect();
assert_eq!(v, [5]);

let x: Result<u32, &str> = Err("nothing!");
let v: Vec<u32> = x.into_iter().collect();
assert_eq!(v, []);

impl<'a, T, E> IntoIterator for &'a Result<T, E>

type Item = &'a T

The type of the elements being iterated over.

type IntoIter = Iter<'a, T>

Which kind of iterator are we turning this into?

pub fn into_iter(self) -> Iter<'a, T>

Creates an iterator from a value.

impl<'a, T, E> IntoParallelIterator for &'a mut Result<T, E> where
    T: Send, 

type Item = &'a mut T

The type of item that the parallel iterator will produce.

type Iter = IterMut<'a, T>

The parallel iterator type that will be created.

pub fn into_par_iter(
    self
) -> <&'a mut Result<T, E> as IntoParallelIterator>::Iter

Converts self into a parallel iterator.

impl<'a, T, E> IntoParallelIterator for &'a Result<T, E> where
    T: Sync, 

type Item = &'a T

The type of item that the parallel iterator will produce.

type Iter = Iter<'a, T>

The parallel iterator type that will be created.

pub fn into_par_iter(self) -> <&'a Result<T, E> as IntoParallelIterator>::Iter

Converts self into a parallel iterator.

impl<T, E> IntoParallelIterator for Result<T, E> where
    T: Send, 

type Item = T

The type of item that the parallel iterator will produce.

type Iter = IntoIter<T>

The parallel iterator type that will be created.

pub fn into_par_iter(self) -> <Result<T, E> as IntoParallelIterator>::Iter

Converts self into a parallel iterator.

impl<T, E> MallocSizeOf for Result<T, E> where
    T: MallocSizeOf,
    E: MallocSizeOf, 

pub fn size_of(&self, ops: &mut MallocSizeOfOps) -> usize

Measure the heap usage of all descendant heap-allocated structures, but not the space taken up by the value itself. If T::size_of is a constant, consider implementing constant_size as well.

pub fn constant_size() -> Option<usize>

Used to optimize MallocSizeOf implementation for collections like Vec and HashMap to avoid iterating over them unnecessarily. The Self: Sized bound is for object safety.

impl<T, E> Ord for Result<T, E> where
    T: Ord,
    E: Ord, 

pub fn cmp(&self, other: &Result<T, E>) -> Ordering

This method returns an Ordering between self and other.

#[must_use]pub fn max(self, other: Self) -> Self

Compares and returns the maximum of two values.

#[must_use]pub fn min(self, other: Self) -> Self

Compares and returns the minimum of two values.

#[must_use]pub fn clamp(self, min: Self, max: Self) -> Self

Restrict a value to a certain interval.

impl<T, E> PartialEq<Result<T, E>> for Result<T, E> where
    T: PartialEq<T>,
    E: PartialEq<E>, 

pub fn eq(&self, other: &Result<T, E>) -> bool

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

pub fn ne(&self, other: &Result<T, E>) -> bool

This method tests for !=.

impl<T, E> PartialOrd<Result<T, E>> for Result<T, E> where
    T: PartialOrd<T>,
    E: PartialOrd<E>, 

pub fn partial_cmp(&self, other: &Result<T, E>) -> Option<Ordering>

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

#[must_use]pub fn lt(&self, other: &Rhs) -> bool

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

#[must_use]pub fn le(&self, other: &Rhs) -> bool

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

#[must_use]pub fn gt(&self, other: &Rhs) -> bool

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

#[must_use]pub 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<T, E> PassBy for Result<T, E> where
    T: Codec,
    E: Codec, 

type PassBy = Codec<Result<T, E>>

The strategy that should be used to pass the type.

impl<T, U, E> Product<Result<U, E>> for Result<T, E> where
    T: Product<U>, 

pub fn product<I>(iter: I) -> Result<T, E> where
    I: Iterator<Item = Result<U, E>>, 

Takes each element in the Iterator: if it is an Err, no further elements are taken, and the Err is returned. Should no Err occur, the product of all elements is returned.

impl<T, E> ResultExt<T, E> for Result<T, E> where
    E: Fail, 

pub fn compat(self) -> Result<T, Compat<E>>

Wraps the error in Compat to make it compatible with older error handling APIs that expect std::error::Error.

pub fn context<D>(self, context: D) -> Result<T, Context<D>> where
    D: Display + Send + Sync + 'static, 

Wraps the error type in a context type.

pub fn with_context<F, D>(self, f: F) -> Result<T, Context<D>> where
    F: FnOnce(&E) -> D,
    D: Display + Send + Sync + 'static, 

Wraps the error type in a context type generated by looking at the error value.

impl<T> ResultExt<T, Error> for Result<T, Error>

pub fn compat(self) -> Result<T, Compat<Error>>

Wraps the error in Compat to make it compatible with older error handling APIs that expect std::error::Error.

pub fn context<D>(self, context: D) -> Result<T, Context<D>> where
    D: Display + Send + Sync + 'static, 

Wraps the error type in a context type.

pub fn with_context<F, D>(self, f: F) -> Result<T, Context<D>> where
    F: FnOnce(&Error) -> D,
    D: Display + Send + Sync + 'static, 

Wraps the error type in a context type generated by looking at the error value.

impl<T, E> Serialize for Result<T, E> where
    T: Serialize,
    E: Serialize, 

pub fn serialize<S>(
    &self,
    serializer: S
) -> Result<<S as Serializer>::Ok, <S as Serializer>::Error> where
    S: Serializer, 

Serialize this value into the given Serde serializer.

impl<T, E> StructuralEq for Result<T, E>

impl<T, E> StructuralPartialEq for Result<T, E>

impl<T, U, E> Sum<Result<U, E>> for Result<T, E> where
    T: Sum<U>, 

pub fn sum<I>(iter: I) -> Result<T, E> where
    I: Iterator<Item = Result<U, E>>, 

Takes each element in the Iterator: if it is an Err, no further elements are taken, and the Err is returned. Should no Err occur, the sum of all elements is returned.

Examples

This sums up every integer in a vector, rejecting the sum if a negative element is encountered:

let v = vec![1, 2];
let res: Result<i32, &'static str> = v.iter().map(|&x: &i32|
    if x < 0 { Err("Negative element found") }
    else { Ok(x) }
).sum();
assert_eq!(res, Ok(3));

impl<E> Termination for Result<!, E> where
    E: Debug, 

pub fn report(self) -> i32

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

Is called to get the representation of the value as status code. This status code is returned to the operating system.

impl<E> Termination for Result<(), E> where
    E: Debug, 

pub fn report(self) -> i32

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

Is called to get the representation of the value as status code. This status code is returned to the operating system.

impl<T, E> Try for Result<T, E>

type Ok = T

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

The type of this value when viewed as successful.

type Error = E

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

The type of this value when viewed as failed.

pub fn into_result(self) -> Result<T, E>

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

Applies the “?” operator. A return of Ok(t) means that the execution should continue normally, and the result of ? is the value t. A return of Err(e) means that execution should branch to the innermost enclosing catch, or return from the function.

pub fn from_ok(v: T) -> Result<T, E>

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

Wrap an OK value to construct the composite result. For example, Result::Ok(x) and Result::from_ok(x) are equivalent.

pub fn from_error(v: E) -> Result<T, E>

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

Wrap an error value to construct the composite result. For example, Result::Err(x) and Result::from_error(x) are equivalent.