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 std::result module documentation for details.
Variants
Ok(T)Contains the success value
Err(E)Contains the error value
Methods
impl<T, E> Result<T, E>[src]
impl<T, E> Result<T, E>pub fn is_ok(&self) -> bool[src]
pub fn is_ok(&self) -> boolReturns 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
pub fn is_err(&self) -> bool[src]
pub fn is_err(&self) -> boolReturns 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
pub fn ok(self) -> Option<T>[src]
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);Run
pub fn err(self) -> Option<E>[src]
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"));Run
pub fn as_ref(&self) -> Result<&T, &E>[src]
pub 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"));Run
pub fn as_mut(&mut self) -> Result<&mut T, &mut E>[src]
pub fn as_mut(&mut self) -> Result<&mut T, &mut E>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
pub fn map<U, F: FnOnce(T) -> U>(self, op: F) -> Result<U, E>[src]
pub fn map<U, F: FnOnce(T) -> U>(self, op: F) -> Result<U, E>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_err<F, O: FnOnce(E) -> F>(self, op: O) -> Result<T, F>[src]
pub fn map_err<F, O: FnOnce(E) -> F>(self, op: O) -> Result<T, 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()));Run
ⓘImportant traits for Iter<'a, T>pub fn iter(&self) -> Iter<T>[src]
pub fn iter(&self) -> Iter<T>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
ⓘImportant traits for IterMut<'a, T>pub fn iter_mut(&mut self) -> IterMut<T>[src]
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 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]
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"));Run
pub fn and_then<U, F: FnOnce(T) -> Result<U, E>>(self, op: F) -> Result<U, E>[src]
pub fn and_then<U, F: FnOnce(T) -> Result<U, E>>(self, op: F) -> 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));Run
pub fn or<F>(self, res: Result<T, F>) -> Result<T, F>[src]
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));Run
pub fn or_else<F, O: FnOnce(E) -> Result<T, F>>(self, op: O) -> Result<T, F>[src]
pub fn or_else<F, O: FnOnce(E) -> Result<T, F>>(self, op: O) -> 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));Run
pub fn unwrap_or(self, optb: T) -> T[src]
pub fn unwrap_or(self, optb: T) -> TUnwraps a result, yielding the content of an Ok.
Else, it returns optb.
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 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
pub fn unwrap_or_else<F: FnOnce(E) -> T>(self, op: F) -> T[src]
pub fn unwrap_or_else<F: FnOnce(E) -> T>(self, op: F) -> Timpl<T, E: Debug> Result<T, E>[src]
impl<T, E: Debug> Result<T, E>pub fn unwrap(self) -> T[src]
pub fn unwrap(self) -> TUnwraps 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
pub fn expect(self, msg: &str) -> T1.4.0[src]
pub fn expect(self, msg: &str) -> TUnwraps 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]
impl<T: Debug, E> Result<T, E>pub fn unwrap_err(self) -> E[src]
pub fn unwrap_err(self) -> EUnwraps 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
pub fn expect_err(self, msg: &str) -> E1.17.0[src]
pub fn expect_err(self, msg: &str) -> EUnwraps 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]
impl<T: Default, E> Result<T, E>pub fn unwrap_or_default(self) -> T1.16.0[src]
pub fn unwrap_or_default(self) -> TReturns 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
impl<T, E> Result<Option<T>, E>[src]
impl<T, E> Result<Option<T>, E>pub fn transpose(self) -> Option<Result<T, E>>[src]
pub 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
#![feature(transpose_result)] #[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
Trait Implementations
impl<T, U, E> Sum<Result<U, E>> for Result<T, E> where
T: Sum<U>, 1.16.0[src]
impl<T, U, E> Sum<Result<U, E>> for Result<T, E> where
T: Sum<U>, fn sum<I>(iter: I) -> Result<T, E> where
I: Iterator<Item = Result<U, E>>, [src]
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));Run
impl<T, U, E> Product<Result<U, E>> for Result<T, E> where
T: Product<U>, 1.16.0[src]
impl<T, U, E> Product<Result<U, E>> for Result<T, E> where
T: Product<U>, fn product<I>(iter: I) -> Result<T, E> where
I: Iterator<Item = Result<U, E>>, [src]
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: Clone, E: Clone> Clone for Result<T, E>[src]
impl<T: Clone, E: Clone> Clone for Result<T, E>fn clone(&self) -> Result<T, E>[src]
fn clone(&self) -> Result<T, E>Returns a copy of the value. Read more
fn clone_from(&mut self, source: &Self)[src]
fn clone_from(&mut self, source: &Self)Performs copy-assignment from source. Read more
impl<T: Copy, E: Copy> Copy for Result<T, E>[src]
impl<T: Copy, E: Copy> Copy for Result<T, E>impl<T: PartialEq, E: PartialEq> PartialEq for Result<T, E>[src]
impl<T: PartialEq, E: PartialEq> PartialEq for Result<T, E>fn eq(&self, other: &Result<T, E>) -> bool[src]
fn eq(&self, other: &Result<T, E>) -> boolThis 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]
fn ne(&self, other: &Result<T, E>) -> boolThis method tests for !=.
impl<T: PartialOrd, E: PartialOrd> PartialOrd for Result<T, E>[src]
impl<T: PartialOrd, E: PartialOrd> PartialOrd for Result<T, E>fn partial_cmp(&self, other: &Result<T, E>) -> Option<Ordering>[src]
fn partial_cmp(&self, other: &Result<T, E>) -> Option<Ordering>This method returns an ordering between self and other values if one exists. Read more
fn lt(&self, other: &Result<T, E>) -> bool[src]
fn lt(&self, other: &Result<T, E>) -> boolThis method tests less than (for self and other) and is used by the < operator. Read more
fn le(&self, other: &Result<T, E>) -> bool[src]
fn le(&self, other: &Result<T, E>) -> boolThis method tests less than or equal to (for self and other) and is used by the <= operator. Read more
fn gt(&self, other: &Result<T, E>) -> bool[src]
fn gt(&self, other: &Result<T, E>) -> boolThis method tests greater than (for self and other) and is used by the > operator. Read more
fn ge(&self, other: &Result<T, E>) -> bool[src]
fn ge(&self, other: &Result<T, E>) -> boolThis 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: Eq, E: Eq> Eq for Result<T, E>impl<T: Ord, E: Ord> Ord for Result<T, E>[src]
impl<T: Ord, E: Ord> Ord for Result<T, E>fn cmp(&self, other: &Result<T, E>) -> Ordering[src]
fn cmp(&self, other: &Result<T, E>) -> OrderingThis method returns an Ordering between self and other. Read more
fn max(self, other: Self) -> Self where
Self: Sized, 1.21.0[src]
fn max(self, other: Self) -> Self where
Self: Sized, Compares and returns the maximum of two values. Read more
fn min(self, other: Self) -> Self where
Self: Sized, 1.21.0[src]
fn min(self, other: Self) -> Self where
Self: Sized, Compares and returns the minimum of two values. Read more
impl<T: Debug, E: Debug> Debug for Result<T, E>[src]
impl<T: Debug, E: Debug> Debug for Result<T, E>fn fmt(&self, f: &mut Formatter) -> Result[src]
fn fmt(&self, f: &mut Formatter) -> ResultFormats the value using the given formatter. Read more
impl<T: Hash, E: Hash> Hash for Result<T, E>[src]
impl<T: Hash, E: Hash> Hash for Result<T, E>fn hash<__HTE: Hasher>(&self, state: &mut __HTE)[src]
fn hash<__HTE: Hasher>(&self, state: &mut __HTE)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]
fn hash_slice<H: Hasher>(data: &[Self], state: &mut H) where
Self: Sized, Feeds a slice of this type into the given [Hasher]. Read more
impl<T, E> IntoIterator for Result<T, E>[src]
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?
ⓘImportant traits for IntoIter<T>fn into_iter(self) -> IntoIter<T>[src]
fn into_iter(self) -> IntoIter<T>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]
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?
ⓘImportant traits for Iter<'a, T>fn into_iter(self) -> Iter<'a, T>[src]
fn into_iter(self) -> Iter<'a, T>Creates an iterator from a value. Read more
impl<'a, T, E> IntoIterator for &'a mut Result<T, E>1.4.0[src]
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?
ⓘImportant traits for IterMut<'a, T>fn into_iter(self) -> IterMut<'a, T>[src]
fn into_iter(self) -> IterMut<'a, T>Creates an iterator from a value. Read more
impl<A, E, V: FromIterator<A>> FromIterator<Result<A, E>> for Result<V, E>[src]
impl<A, E, V: FromIterator<A>> FromIterator<Result<A, E>> for Result<V, E>fn from_iter<I: IntoIterator<Item = Result<A, E>>>(iter: I) -> Result<V, E>[src]
fn from_iter<I: IntoIterator<Item = Result<A, E>>>(iter: I) -> Result<V, 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!(res == Ok(vec![2, 3]));Run
impl<T, E> Try for Result<T, E>[src]
impl<T, E> Try for Result<T, E>type Ok = T
The type of this value when viewed as successful.
type Error = E
The type of this value when viewed as failed.
fn into_result(self) -> Self[src]
fn into_result(self) -> SelfApplies 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]
fn from_ok(v: T) -> SelfWrap 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]
fn from_error(v: E) -> SelfWrap an error value to construct the composite result. For example, Result::Err(x) and Result::from_error(x) are equivalent. Read more