Enum core::result::Result1.0.0 [] [src]

#[must_use]
pub enum Result<T, E> { Ok(T), Err(E), }

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

See the std::result module documentation for details.

Variants

Contains the success value

Contains the error value

Methods

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

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

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

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

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

Converts from 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

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

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

Returns an iterator over the possibly contained value.

The iterator yields one value if the result is 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

Returns a mutable iterator over the possibly contained value.

The iterator yields one value if the result is 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

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

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

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

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

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

Unwraps a result, yielding the content of an Ok. Else, it returns optb.

Examples

Basic usage:

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

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

Unwraps a result, yielding the content of an Ok. If the value is an Err then it calls op with its value.

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

impl<T, E: Debug> Result<T, E>
[src]

Unwraps a result, yielding the content of an Ok.

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

Unwraps a result, yielding the content of an Ok.

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

impl<T: Debug, E> Result<T, E>
[src]

Unwraps a result, yielding the content of an Err.

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

Unwraps a result, yielding the content of an Err.

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

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

Returns the contained 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

Convert 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

Trait Implementations

impl<U, V> Carrier for Result<U, V>
[src]

🔬 This is a nightly-only experimental API. (question_mark_carrier #31436)

The type of the value when computation succeeds.

🔬 This is a nightly-only experimental API. (question_mark_carrier #31436)

The type of the value when computation errors out.

🔬 This is a nightly-only experimental API. (question_mark_carrier #31436)

Create a Carrier from a success value.

🔬 This is a nightly-only experimental API. (question_mark_carrier #31436)

Create a Carrier from an error value.

🔬 This is a nightly-only experimental API. (question_mark_carrier #31436)

Translate this Carrier to another implementation of Carrier with the same associated types. Read more

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

Method which takes an iterator and generates Self from the elements by "summing up" the items. Read more

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

Method which takes an iterator and generates Self from the elements by multiplying the items. Read more

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

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

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

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

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

This method tests for !=.

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

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

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

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

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

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

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

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

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

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

Formats the value using the given formatter.

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

Feeds this value into the state given, updating the hasher as necessary.

Feeds a slice of this type into the state provided.

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

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

Returns a consuming iterator over the possibly contained value.

The iterator yields one value if the result is 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]

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

Creates an iterator from a value. Read more

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

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

Creates an iterator from a value. Read more

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

use std::u32;

let v = vec![1, 2];
let res: Result<Vec<u32>, &'static str> = v.iter().map(|&x: &u32|
    if x == u32::MAX { Err("Overflow!") }
    else { Ok(x + 1) }
).collect();
assert!(res == Ok(vec![2, 3]));Run