# Enum core::result::Result 1.0.0[−][src]

    #[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>`[src]

#### `#[must_use = "if you intended to assert that this is ok, consider `.unwrap()` instead"]pub const fn is_ok(&self) -> bool` 1.0.0 (const: 1.48.0)[src]

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);

Run

#### `#[must_use = "if you intended to assert that this is err, consider `.unwrap_err()` instead"]pub const fn is_err(&self) -> bool` 1.0.0 (const: 1.48.0)[src]

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);

Run

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

🔬 This is a nightly-only experimental API. (`option_result_contains` #62358)

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);

Run

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

🔬 This is a nightly-only experimental API. (`result_contains_err` #62358)

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);

Run

#### `pub fn ok(self) -> Option<T>`[src]

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);

Run

#### `pub fn err(self) -> Option<E>`[src]

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"));

Run

#### `pub const fn as_ref(&self) -> Result<&T, &E>`1.0.0 (const: 1.48.0)[src]

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"));

Run

#### `pub fn as_mut(&mut self) -> Result<&mut T, &mut E>`[src]

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);

Run

#### `pub fn map<U, F: FnOnce(T) -> U>(self, op: F) -> Result<U, E>`[src]

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(..) => {}
        }
    }

Run

#### `pub fn map_or<U, F: FnOnce(T) -> U>(self, default: U, f: F) -> U` 1.41.0[src]

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);

Run

#### `pub fn map_or_else<U, D: FnOnce(E) -> U, F: FnOnce(T) -> U>(
self,
default: D,
f: F
) -> U` 1.41.0[src]

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);

Run

#### `pub fn map_err<F, O: FnOnce(E) -> F>(self, op: O) -> Result<T, F>`[src]

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()));

Run

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

### Notable traits for Iter<'a, T>

`impl<'a, T> Iterator for Iter<'a, T> type Item = &'a T;`
`[src]

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);

Run

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

### Notable traits for IterMut<'a, T>

`impl<'a, T> Iterator for IterMut<'a, T> type Item = &'a mut T;`
`[src]

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);

Run

#### `pub fn and<U>(self, res: Result<U, E>) -> Result<U, E>`[src]

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"));

Run

#### `pub fn and_then<U, F: FnOnce(T) -> Result<U, E>>(self, op: F) -> Result<U, E>`[src]

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));

Run

#### `pub fn or<F>(self, res: Result<T, F>) -> Result<T, F>`[src]

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));

Run

#### `pub fn or_else<F, O: FnOnce(E) -> Result<T, F>>(self, op: O) -> Result<T, F>`[src]

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));

Run

#### `pub fn unwrap_or(self, default: T) -> T`[src]

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);

Run

#### `pub fn unwrap_or_else<F: FnOnce(E) -> T>(self, op: F) -> T`[src]

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);

Run

#### `pub unsafe fn unwrap_unchecked(self) -> T`[src]

🔬 This is a nightly-only experimental API. (`option_result_unwrap_unchecked` #81383)

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);

Run

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

Run

#### `pub unsafe fn unwrap_err_unchecked(self) -> E`[src]

🔬 This is a nightly-only experimental API. (`option_result_unwrap_unchecked` #81383)

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!

Run

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

Run

### `impl<T: Copy, E> Result<&T, E>`[src]

#### `pub fn copied(self) -> Result<T, E>`[src]

🔬 This is a nightly-only experimental API. (`result_copied` #63168)

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));

Run

### `impl<T: Copy, E> Result<&mut T, E>`[src]

#### `pub fn copied(self) -> Result<T, E>`[src]

🔬 This is a nightly-only experimental API. (`result_copied` #63168)

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));

Run

### `impl<T: Clone, E> Result<&T, E>`[src]

#### `pub fn cloned(self) -> Result<T, E>`[src]

🔬 This is a nightly-only experimental API. (`result_cloned` #63168)

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));

Run

### `impl<T: Clone, E> Result<&mut T, E>`[src]

#### `pub fn cloned(self) -> Result<T, E>`[src]

🔬 This is a nightly-only experimental API. (`result_cloned` #63168)

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));

Run

### `impl<T, E: Debug> Result<T, E>`[src]

#### `pub fn expect(self, msg: &str) -> T` 1.4.0[src]

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`

Run

#### `pub fn unwrap(self) -> T`[src]

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);

Run
ⓘ

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

Run

### `impl<T: Debug, E> Result<T, E>`[src]

#### `pub fn expect_err(self, msg: &str) -> E` 1.17.0[src]

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`

Run

#### `pub fn unwrap_err(self) -> E`[src]

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`

Run

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

Run

### `impl<T: Default, E> Result<T, E>`[src]

#### `pub fn unwrap_or_default(self) -> T` 1.16.0[src]

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);

Run

### `impl<T, E: Into<!>> Result<T, E>`[src]

#### `pub fn into_ok(self) -> T`[src]

🔬 This is a nightly-only experimental API. (`unwrap_infallible` #61695)

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);

Run

### `impl<T: Deref, E> Result<T, E>`[src]

#### `pub fn as_deref(&self) -> Result<&T::Target, &E>`1.47.0[src]

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);

Run

### `impl<T: DerefMut, E> Result<T, E>`[src]

#### `pub fn as_deref_mut(&mut self) -> Result<&mut T::Target, &mut E>`1.47.0[src]

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);

Run

### `impl<T, E> Result<Option<T>, E>`[src]

#### `pub fn transpose(self) -> Option<Result<T, E>>`1.33.0[src]

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);

Run

### `impl<T, E> Result<Result<T, E>, E>`[src]

#### `pub fn flatten(self) -> Result<T, E>`[src]

🔬 This is a nightly-only experimental API. (`result_flattening` #70142)

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());

Run

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());

Run

## Trait Implementations

### `impl<T: Clone, E: Clone> Clone for Result<T, E>`[src]

#### `fn clone(&self) -> Self`[src]

Returns a copy of the value. Read more

#### `fn clone_from(&mut self, source: &Self)`[src]

Performs copy-assignment from `source`. Read more

### `impl<T: Copy, E: Copy> Copy for Result<T, E>`[src]

### `impl<T: Debug, E: Debug> Debug for Result<T, E>`[src]

#### `fn fmt(&self, f: &mut Formatter<'_>) -> Result`[src]

Formats the value using the given formatter. Read more

### `impl<T: Eq, E: Eq> Eq for Result<T, E>`[src]

### `impl<A, E, V: FromIterator<A>> FromIterator<Result<A, E>> for Result<V, E>`[src]

#### `fn from_iter<I: IntoIterator<Item = Result<A, E>>>(iter: I) -> Result<V, E>`[src]

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]));

Run

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!"));

Run

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);

Run

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<T: Hash, E: Hash> Hash for Result<T, E>`[src]

#### `fn hash<__H: Hasher>(&self, state: &mut __H)`[src]

Feeds this value into the given `Hasher`. Read more

#### `fn hash_slice<H: Hasher>(data: &[Self], state: &mut H) where
Self: Sized,` 1.3.0[src]

Feeds a slice of this type into the given `Hasher`. Read more

### `impl<T, E> IntoIterator for Result<T, E>`[src]

#### `type Item = T`

The type of the elements being iterated over.

#### `type IntoIter = IntoIter<T>`

Which kind of iterator are we turning this into?

#### `fn into_iter(self) -> IntoIter<T>ⓘ

### Notable traits for IntoIter<T>

`impl<T> Iterator for IntoIter<T> type Item = T;`
`[src]

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, []);

Run

### `impl<'a, T, E> IntoIterator for &'a Result<T, E>`1.4.0[src]

#### `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?

#### `fn into_iter(self) -> Iter<'a, T>ⓘ

### Notable traits for Iter<'a, T>

`impl<'a, T> Iterator for Iter<'a, T> type Item = &'a T;`
`[src]

Creates an iterator from a value. Read more

### `impl<'a, T, E> IntoIterator for &'a mut Result<T, E>`1.4.0[src]

#### `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?

#### `fn into_iter(self) -> IterMut<'a, T>ⓘ

### Notable traits for IterMut<'a, T>

`impl<'a, T> Iterator for IterMut<'a, T> type Item = &'a mut T;`
`[src]

Creates an iterator from a value. Read more

### `impl<T: Ord, E: Ord> Ord for Result<T, E>`[src]

#### `fn cmp(&self, other: &Result<T, E>) -> Ordering`[src]

This method returns an `Ordering` between `self` and `other`. Read more

#### `#[must_use]fn max(self, other: Self) -> Self where
Self: Sized,` 1.21.0[src]

Compares and returns the maximum of two values. Read more

#### `#[must_use]fn min(self, other: Self) -> Self where
Self: Sized,` 1.21.0[src]

Compares and returns the minimum of two values. Read more

#### `#[must_use]fn clamp(self, min: Self, max: Self) -> Self where
Self: Sized,` 1.50.0[src]

Restrict a value to a certain interval. Read more

### `impl<T: PartialEq, E: PartialEq> PartialEq<Result<T, E>> for Result<T, E>`[src]

#### `fn eq(&self, other: &Result<T, E>) -> bool`[src]

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

#### `fn ne(&self, other: &Result<T, E>) -> bool`[src]

This method tests for `!=`.

### `impl<T: PartialOrd, E: PartialOrd> PartialOrd<Result<T, E>> for Result<T, E>`[src]

#### `fn partial_cmp(&self, other: &Result<T, E>) -> Option<Ordering>`[src]

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

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

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

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

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

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

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

#### `#[must_use]fn ge(&self, other: &Rhs) -> bool`[src]

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

### `impl<T, U, E> Product<Result<U, E>> for Result<T, E> where
T: Product<U>,` 1.16.0[src]

#### `fn product<I>(iter: I) -> Result<T, E> where
I: Iterator<Item = Result<U, E>>,` [src]

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> StructuralEq for Result<T, E>`[src]

### `impl<T, E> StructuralPartialEq for Result<T, E>`[src]

### `impl<T, U, E> Sum<Result<U, E>> for Result<T, E> where
T: Sum<U>,` 1.16.0[src]

#### `fn sum<I>(iter: I) -> Result<T, E> where
I: Iterator<Item = Result<U, E>>,` [src]

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));

Run

### `impl<T, E> Try for Result<T, E>`[src]

#### `type Ok = T`

🔬 This is a nightly-only experimental API. (`try_trait` #42327)

The type of this value when viewed as successful.

#### `type Error = E`

🔬 This is a nightly-only experimental API. (`try_trait` #42327)

The type of this value when viewed as failed.

#### `fn into_result(self) -> Self`[src]

🔬 This is a nightly-only experimental API. (`try_trait` #42327)

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. Read more

#### `fn from_ok(v: T) -> Self`[src]

🔬 This is a nightly-only experimental API. (`try_trait` #42327)

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

#### `fn from_error(v: E) -> Self`[src]

🔬 This is a nightly-only experimental API. (`try_trait` #42327)

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

## Auto Trait Implementations

### `impl<T, E> Send for Result<T, E> where
E: Send,
T: Send,` [src]

### `impl<T, E> Sync for Result<T, E> where
E: Sync,
T: Sync,` [src]

### `impl<T, E> Unpin for Result<T, E> where
E: Unpin,
T: Unpin,` [src]

## Blanket Implementations

### `impl<T> Any for T where
T: 'static + ?Sized,` [src]

#### `pub fn type_id(&Self) -> TypeId`[src]

Gets the `TypeId` of `self`. Read more

### `impl<T> Borrow<T> for T where
T: ?Sized,` [src]

#### `pub fn borrow(&Self) -> &T`[src]

Immutably borrows from an owned value. Read more

### `impl<T> BorrowMut<T> for T where
T: ?Sized,` [src]

#### `pub fn borrow_mut(&mut Self) -> &mut T`[src]

Mutably borrows from an owned value. Read more

### `impl<T> From<T> for T`[src]

#### `pub fn from(T) -> T`[src]

Performs the conversion.

### `impl<T, U> Into<U> for T where
U: From<T>,` [src]

#### `pub fn into(Self) -> U`[src]

Performs the conversion.

### `impl<T, U> TryFrom<U> for T where
U: Into<T>,` [src]

#### `type Error = Infallible`

The type returned in the event of a conversion error.

#### `pub fn try_from(U) -> Result<T, <T as TryFrom<U>>::Error>`[src]

Performs the conversion.

### `impl<T, U> TryInto<U> for T where
U: TryFrom<T>,` [src]

#### `type Error = <U as TryFrom<T>>::Error`

The type returned in the event of a conversion error.

#### `pub fn try_into(Self) -> Result<U, <U as TryFrom<T>>::Error>`[src]

Performs the conversion.