Enum std::result::Result [−] [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

`Ok`	Contains the success value
`Err`	Contains the error value

Methods

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

`fn is_ok(&self) -> bool`

Returns true if the result is Ok

Examples

fn main() { 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); }

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);

`fn is_err(&self) -> bool`

Returns true if the result is Err

Examples

fn main() { 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); }

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);

`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

fn main() { 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); }

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);

`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

fn main() { 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")); }

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"));

`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.

fn main() { 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")); }

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"));

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

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

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

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

`fn as_slice(&self) -> &[T]`

Deprecated since 1.4.0
: niche API, unclear of usefulness

Converts from Result<T, E> to &[T] (without copying)

`fn as_mut_slice(&mut self) -> &mut [T]`

Deprecated since 1.4.0
: niche API, unclear of usefulness

Converts from Result<T, E> to &mut [T] (without copying)

#![feature(as_slice)] fn main() { #![allow(deprecated)] let mut x: Result<&str, u32> = Ok("Gold"); { let v = x.as_mut_slice(); assert!(v == ["Gold"]); v[0] = "Silver"; assert!(v == ["Silver"]); } assert_eq!(x, Ok("Silver")); let mut x: Result<&str, u32> = Err(45); assert!(x.as_mut_slice().is_empty()); }

#![feature(as_slice)]

let mut x: Result<&str, u32> = Ok("Gold");
{
    let v = x.as_mut_slice();
    assert!(v == ["Gold"]);
    v[0] = "Silver";
    assert!(v == ["Silver"]);
}
assert_eq!(x, Ok("Silver"));

let mut x: Result<&str, u32> = Err(45);
assert!(x.as_mut_slice().is_empty());

`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.

fn main() { 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(..) => {} } } }

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(..) => {}
    }
}

`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

fn main() { 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())); }

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()));

`fn iter(&self) -> Iter<T>`

Returns an iterator over the possibly contained value.

Examples

fn main() { 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); }

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);

`fn iter_mut(&mut self) -> IterMut<T>`

Returns a mutable iterator over the possibly contained value.

Examples

fn main() { 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); }

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);

`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

fn main() { 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")); }

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"));

`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

fn main() { 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)); }

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));

`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.

Examples

fn main() { 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)); }

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));

`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

fn main() { 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)); }

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));

`fn unwrap_or(self, optb: T) -> T`

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

Examples

fn main() { 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); }

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);

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

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

Examples

fn main() { 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); }

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);

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

`fn unwrap(self) -> T`

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

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

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

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

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

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

Unwraps a result, yielding the content of an Ok.

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

Examples

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

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

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

`fn unwrap_err(self) -> E`

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

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

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

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

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

Enum std::result::Result [−] [src]

Variants

Methods

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

fn is_ok(&self) -> bool

fn is_err(&self) -> bool

fn ok(self) -> Option<T>

fn err(self) -> Option<E>

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

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

fn as_slice(&self) -> &[T]

fn as_mut_slice(&mut self) -> &mut [T]

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

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

fn iter(&self) -> Iter<T>

fn iter_mut(&mut self) -> IterMut<T>

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

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

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

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

fn unwrap_or(self, optb: T) -> T

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

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

fn unwrap(self) -> T

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

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

fn unwrap_err(self) -> E

Trait Implementations

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

type Item = T

type IntoIter = IntoIter<T>

fn into_iter(self) -> IntoIter<T>

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

type Item = &'a T

type IntoIter = Iter<'a, T>

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

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

type Item = &'a mut T

type IntoIter = IterMut<'a, T>

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

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

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

Derived Implementations

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

fn hash<__H>(&self, __arg_0: &mut __H) where __H: Hasher

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

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

fn fmt(&self, __arg_0: &mut Formatter) -> Result<(), Error>

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

fn cmp(&self, __arg_0: &Result<T, E>) -> Ordering

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

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

fn partial_cmp(&self, __arg_0: &Result<T, E>) -> Option<Ordering>

fn lt(&self, __arg_0: &Result<T, E>) -> bool

fn le(&self, __arg_0: &Result<T, E>) -> bool

fn gt(&self, __arg_0: &Result<T, E>) -> bool

fn ge(&self, __arg_0: &Result<T, E>) -> bool

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

fn eq(&self, __arg_0: &Result<T, E>) -> bool

fn ne(&self, __arg_0: &Result<T, E>) -> bool

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

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

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

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

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

`fn is_ok(&self) -> bool`

`fn is_err(&self) -> bool`

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

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

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

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

`fn as_slice(&self) -> &[T]`

`fn as_mut_slice(&mut self) -> &mut [T]`

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

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

`fn iter(&self) -> Iter<T>`

`fn iter_mut(&mut self) -> IterMut<T>`

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

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

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

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

`fn unwrap_or(self, optb: T) -> T`

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

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

`fn unwrap(self) -> T`

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

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

`fn unwrap_err(self) -> E`

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

`type Item = T`

`type IntoIter = IntoIter<T>`

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

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

`type Item = &'a T`

`type IntoIter = Iter<'a, T>`

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

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

`type Item = &'a mut T`

`type IntoIter = IterMut<'a, T>`

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

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

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

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

`fn hash<H>(&self, arg_0: &mut H) where H: Hasher`

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

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

`fn fmt(&self, __arg_0: &mut Formatter) -> Result<(), Error>`

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

`fn cmp(&self, __arg_0: &Result<T, E>) -> Ordering`

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

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

`fn partial_cmp(&self, __arg_0: &Result<T, E>) -> Option<Ordering>`

`fn lt(&self, __arg_0: &Result<T, E>) -> bool`

`fn le(&self, __arg_0: &Result<T, E>) -> bool`

`fn gt(&self, __arg_0: &Result<T, E>) -> bool`

`fn ge(&self, __arg_0: &Result<T, E>) -> bool`

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

`fn eq(&self, __arg_0: &Result<T, E>) -> bool`

`fn ne(&self, __arg_0: &Result<T, E>) -> bool`

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

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

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

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