1.0.0[−][src]Enum core::option::Option
The Option type. See the module level documentation for more.
Variants
NoneNo value
Some(T)Some value T
Methods
impl<T> Option<T>[src]
pub fn is_some(&self) -> bool[src]
Returns true if the option is a Some value.
Examples
let x: Option<u32> = Some(2); assert_eq!(x.is_some(), true); let x: Option<u32> = None; assert_eq!(x.is_some(), false);Run
pub fn is_none(&self) -> bool[src]
Returns true if the option is a None value.
Examples
let x: Option<u32> = Some(2); assert_eq!(x.is_none(), false); let x: Option<u32> = None; assert_eq!(x.is_none(), true);Run
pub fn as_ref(&self) -> Option<&T>[src]
Converts from Option<T> to Option<&T>.
Examples
Converts an Option<String> into an Option<usize>, preserving the original.
The map method takes the self argument by value, consuming the original,
so this technique uses as_ref to first take an Option to a reference
to the value inside the original.
let text: Option<String> = Some("Hello, world!".to_string()); // First, cast `Option<String>` to `Option<&String>` with `as_ref`, // then consume *that* with `map`, leaving `text` on the stack. let text_length: Option<usize> = text.as_ref().map(|s| s.len()); println!("still can print text: {:?}", text);Run
pub fn as_mut(&mut self) -> Option<&mut T>[src]
Converts from Option<T> to Option<&mut T>.
Examples
let mut x = Some(2); match x.as_mut() { Some(v) => *v = 42, None => {}, } assert_eq!(x, Some(42));Run
pub fn as_pin_ref<'a>(self: Pin<&'a Option<T>>) -> Option<Pin<&'a T>>1.33.0[src]
Converts from Pin<&Option<T>> to Option<Pin<&T>>
pub fn as_pin_mut<'a>(self: Pin<&'a mut Option<T>>) -> Option<Pin<&'a mut T>>1.33.0[src]
Converts from Pin<&mut Option<T>> to Option<Pin<&mut T>>
pub fn expect(self, msg: &str) -> T[src]
Unwraps an option, yielding the content of a Some.
Panics
Panics if the value is a None with a custom panic message provided by
msg.
Examples
let x = Some("value"); assert_eq!(x.expect("the world is ending"), "value");Run
let x: Option<&str> = None; x.expect("the world is ending"); // panics with `the world is ending`Run
pub fn unwrap(self) -> T[src]
Moves the value v out of the Option<T> if it is Some(v).
In general, because this function may panic, its use is discouraged.
Instead, prefer to use pattern matching and handle the None
case explicitly.
Panics
Panics if the self value equals None.
Examples
let x = Some("air"); assert_eq!(x.unwrap(), "air");Run
let x: Option<&str> = None; assert_eq!(x.unwrap(), "air"); // failsRun
pub fn unwrap_or(self, def: T) -> T[src]
Returns the contained value or a 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
assert_eq!(Some("car").unwrap_or("bike"), "car"); assert_eq!(None.unwrap_or("bike"), "bike");Run
pub fn unwrap_or_else<F: FnOnce() -> T>(self, f: F) -> T[src]
Returns the contained value or computes it from a closure.
Examples
let k = 10; assert_eq!(Some(4).unwrap_or_else(|| 2 * k), 4); assert_eq!(None.unwrap_or_else(|| 2 * k), 20);Run
pub fn map<U, F: FnOnce(T) -> U>(self, f: F) -> Option<U>[src]
Maps an Option<T> to Option<U> by applying a function to a contained value.
Examples
Converts an Option<String> into an Option<usize>, consuming the original:
let maybe_some_string = Some(String::from("Hello, World!")); // `Option::map` takes self *by value*, consuming `maybe_some_string` let maybe_some_len = maybe_some_string.map(|s| s.len()); assert_eq!(maybe_some_len, Some(13));Run
pub fn map_or<U, F: FnOnce(T) -> U>(self, default: U, f: F) -> U[src]
Applies a function to the contained value (if any), or returns the provided default (if not).
Examples
let x = Some("foo"); assert_eq!(x.map_or(42, |v| v.len()), 3); let x: Option<&str> = None; assert_eq!(x.map_or(42, |v| v.len()), 42);Run
pub fn map_or_else<U, D: FnOnce() -> U, F: FnOnce(T) -> U>(
self,
default: D,
f: F
) -> U[src]
self,
default: D,
f: F
) -> U
Applies a function to the contained value (if any), or computes a default (if not).
Examples
let k = 21; let x = Some("foo"); assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 3); let x: Option<&str> = None; assert_eq!(x.map_or_else(|| 2 * k, |v| v.len()), 42);Run
pub fn ok_or<E>(self, err: E) -> Result<T, E>[src]
Transforms the Option<T> into a Result<T, E>, mapping Some(v) to
Ok(v) and None to Err(err).
Arguments passed to ok_or are eagerly evaluated; if you are passing the
result of a function call, it is recommended to use ok_or_else, which is
lazily evaluated.
Examples
let x = Some("foo"); assert_eq!(x.ok_or(0), Ok("foo")); let x: Option<&str> = None; assert_eq!(x.ok_or(0), Err(0));Run
pub fn ok_or_else<E, F: FnOnce() -> E>(self, err: F) -> Result<T, E>[src]
Transforms the Option<T> into a Result<T, E>, mapping Some(v) to
Ok(v) and None to Err(err()).
Examples
let x = Some("foo"); assert_eq!(x.ok_or_else(|| 0), Ok("foo")); let x: Option<&str> = None; assert_eq!(x.ok_or_else(|| 0), Err(0));Run
ⓘImportant traits for Iter<'a, A>pub fn iter(&self) -> Iter<T>[src]
Returns an iterator over the possibly contained value.
Examples
let x = Some(4); assert_eq!(x.iter().next(), Some(&4)); let x: Option<u32> = None; assert_eq!(x.iter().next(), None);Run
ⓘImportant traits for IterMut<'a, A>pub fn iter_mut(&mut self) -> IterMut<T>[src]
Returns a mutable iterator over the possibly contained value.
Examples
let mut x = Some(4); match x.iter_mut().next() { Some(v) => *v = 42, None => {}, } assert_eq!(x, Some(42)); let mut x: Option<u32> = None; assert_eq!(x.iter_mut().next(), None);Run
pub fn and<U>(self, optb: Option<U>) -> Option<U>[src]
Returns None if the option is None, otherwise returns optb.
Examples
let x = Some(2); let y: Option<&str> = None; assert_eq!(x.and(y), None); let x: Option<u32> = None; let y = Some("foo"); assert_eq!(x.and(y), None); let x = Some(2); let y = Some("foo"); assert_eq!(x.and(y), Some("foo")); let x: Option<u32> = None; let y: Option<&str> = None; assert_eq!(x.and(y), None);Run
pub fn and_then<U, F: FnOnce(T) -> Option<U>>(self, f: F) -> Option<U>[src]
Returns None if the option is None, otherwise calls f with the
wrapped value and returns the result.
Some languages call this operation flatmap.
Examples
fn sq(x: u32) -> Option<u32> { Some(x * x) } fn nope(_: u32) -> Option<u32> { None } assert_eq!(Some(2).and_then(sq).and_then(sq), Some(16)); assert_eq!(Some(2).and_then(sq).and_then(nope), None); assert_eq!(Some(2).and_then(nope).and_then(sq), None); assert_eq!(None.and_then(sq).and_then(sq), None);Run
pub fn filter<P: FnOnce(&T) -> bool>(self, predicate: P) -> Self1.27.0[src]
Returns None if the option is None, otherwise calls predicate
with the wrapped value and returns:
Some(t)ifpredicatereturnstrue(wheretis the wrapped value), andNoneifpredicatereturnsfalse.
This function works similar to Iterator::filter(). You can imagine
the Option<T> being an iterator over one or zero elements. filter()
lets you decide which elements to keep.
Examples
fn is_even(n: &i32) -> bool { n % 2 == 0 } assert_eq!(None.filter(is_even), None); assert_eq!(Some(3).filter(is_even), None); assert_eq!(Some(4).filter(is_even), Some(4));Run
pub fn or(self, optb: Option<T>) -> Option<T>[src]
Returns the option if it contains a value, otherwise returns optb.
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
let x = Some(2); let y = None; assert_eq!(x.or(y), Some(2)); let x = None; let y = Some(100); assert_eq!(x.or(y), Some(100)); let x = Some(2); let y = Some(100); assert_eq!(x.or(y), Some(2)); let x: Option<u32> = None; let y = None; assert_eq!(x.or(y), None);Run
pub fn or_else<F: FnOnce() -> Option<T>>(self, f: F) -> Option<T>[src]
Returns the option if it contains a value, otherwise calls f and
returns the result.
Examples
fn nobody() -> Option<&'static str> { None } fn vikings() -> Option<&'static str> { Some("vikings") } assert_eq!(Some("barbarians").or_else(vikings), Some("barbarians")); assert_eq!(None.or_else(vikings), Some("vikings")); assert_eq!(None.or_else(nobody), None);Run
pub fn xor(self, optb: Option<T>) -> Option<T>[src]
Returns Some if exactly one of self, optb is Some, otherwise returns None.
Examples
#![feature(option_xor)] let x = Some(2); let y: Option<u32> = None; assert_eq!(x.xor(y), Some(2)); let x: Option<u32> = None; let y = Some(2); assert_eq!(x.xor(y), Some(2)); let x = Some(2); let y = Some(2); assert_eq!(x.xor(y), None); let x: Option<u32> = None; let y: Option<u32> = None; assert_eq!(x.xor(y), None);Run
pub fn get_or_insert(&mut self, v: T) -> &mut T1.20.0[src]
Inserts v into the option if it is None, then
returns a mutable reference to the contained value.
Examples
let mut x = None; { let y: &mut u32 = x.get_or_insert(5); assert_eq!(y, &5); *y = 7; } assert_eq!(x, Some(7));Run
pub fn get_or_insert_with<F: FnOnce() -> T>(&mut self, f: F) -> &mut T1.20.0[src]
Inserts a value computed from f into the option if it is None, then
returns a mutable reference to the contained value.
Examples
let mut x = None; { let y: &mut u32 = x.get_or_insert_with(|| 5); assert_eq!(y, &5); *y = 7; } assert_eq!(x, Some(7));Run
pub fn take(&mut self) -> Option<T>[src]
Takes the value out of the option, leaving a None in its place.
Examples
let mut x = Some(2); let y = x.take(); assert_eq!(x, None); assert_eq!(y, Some(2)); let mut x: Option<u32> = None; let y = x.take(); assert_eq!(x, None); assert_eq!(y, None);Run
pub fn replace(&mut self, value: T) -> Option<T>1.31.0[src]
Replaces the actual value in the option by the value given in parameter,
returning the old value if present,
leaving a Some in its place without deinitializing either one.
Examples
let mut x = Some(2); let old = x.replace(5); assert_eq!(x, Some(5)); assert_eq!(old, Some(2)); let mut x = None; let old = x.replace(3); assert_eq!(x, Some(3)); assert_eq!(old, None);Run
impl<T: Copy, '_> Option<&'_ T>[src]
impl<T: Copy, '_> Option<&'_ mut T>[src]
impl<T: Clone, '_> Option<&'_ T>[src]
impl<T: Clone, '_> Option<&'_ mut T>[src]
impl<T: Default> Option<T>[src]
pub fn unwrap_or_default(self) -> T[src]
Returns the contained value or a default
Consumes the self argument then, if Some, returns the contained
value, otherwise if None, 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
None on error.
let good_year_from_input = "1909"; let bad_year_from_input = "190blarg"; let good_year = good_year_from_input.parse().ok().unwrap_or_default(); let bad_year = bad_year_from_input.parse().ok().unwrap_or_default(); assert_eq!(1909, good_year); assert_eq!(0, bad_year);Run
impl<T: Deref> Option<T>[src]
pub fn deref(&self) -> Option<&T::Target>[src]
🔬 This is a nightly-only experimental API. (inner_deref #50264)
newly added
Converts from &Option<T> to Option<&T::Target>.
Leaves the original Option in-place, creating a new one with a reference
to the original one, additionally coercing the contents via Deref.
impl<T, E> Option<Result<T, E>>[src]
pub fn transpose(self) -> Result<Option<T>, E>1.33.0[src]
Transposes an Option of a Result into a Result of an Option.
None will be mapped to Ok(None).
Some(Ok(_)) and Some(Err(_)) will be mapped to Ok(Some(_)) and 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, y.transpose());Run
Trait Implementations
impl<T: Copy> Copy for Option<T>[src]
impl<T> Try for Option<T>[src]
type Ok = T
The type of this value when viewed as successful.
type Error = NoneError
The type of this value when viewed as failed.
fn into_result(self) -> Result<T, NoneError>[src]
fn from_ok(v: T) -> Self[src]
fn from_error(_: NoneError) -> Self[src]
impl<T: PartialEq> PartialEq<Option<T>> for Option<T>[src]
impl<T: Eq> Eq for Option<T>[src]
impl<T: Ord> Ord for Option<T>[src]
fn cmp(&self, other: &Option<T>) -> Ordering[src]
fn max(self, other: Self) -> Self where
Self: Sized, 1.21.0[src]
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]
Self: Sized,
Compares and returns the minimum of two values. Read more
impl<T: PartialOrd> PartialOrd<Option<T>> for Option<T>[src]
fn partial_cmp(&self, other: &Option<T>) -> Option<Ordering>[src]
fn lt(&self, other: &Option<T>) -> bool[src]
fn le(&self, other: &Option<T>) -> bool[src]
fn gt(&self, other: &Option<T>) -> bool[src]
fn ge(&self, other: &Option<T>) -> bool[src]
impl<T: Clone> Clone for Option<T>[src]
fn clone(&self) -> Option<T>[src]
fn clone_from(&mut self, source: &Self)[src]
Performs copy-assignment from source. Read more
impl<T> Default for Option<T>[src]
impl<T> From<T> for Option<T>1.12.0[src]
impl<'a, T> From<&'a Option<T>> for Option<&'a T>1.30.0[src]
impl<'a, T> From<&'a mut Option<T>> for Option<&'a mut T>1.30.0[src]
impl<A, V: FromIterator<A>> FromIterator<Option<A>> for Option<V>[src]
fn from_iter<I: IntoIterator<Item = Option<A>>>(iter: I) -> Option<V>[src]
Takes each element in the Iterator: if it is None,
no further elements are taken, and the None is
returned. Should no None occur, a container with the
values of each Option is returned.
Examples
Here is an example which increments every integer in a vector.
We use the checked variant ofaddthat returnsNone` when the
calculation would result in an overflow.
let items = vec![0_u16, 1, 2]; let res: Option<Vec<u16>> = items .iter() .map(|x| x.checked_add(1)) .collect(); assert_eq!(res, Some(vec![1, 2, 3]));Run
As you can see, this will return the expected, valid items.
Here is another example that tries to subtract one from another list of integers, this time checking for underflow:
let items = vec![2_u16, 1, 0]; let res: Option<Vec<u16>> = items .iter() .map(|x| x.checked_sub(1)) .collect(); assert_eq!(res, None);Run
Since the last element is zero, it would underflow. Thus, the resulting
value is None.
impl<T> IntoIterator for Option<T>[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?
ⓘImportant traits for IntoIter<A>fn into_iter(self) -> IntoIter<T>[src]
impl<'a, T> IntoIterator for &'a Option<T>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?
ⓘImportant traits for Iter<'a, A>fn into_iter(self) -> Iter<'a, T>[src]
impl<'a, T> IntoIterator for &'a mut Option<T>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?
ⓘImportant traits for IterMut<'a, A>fn into_iter(self) -> IterMut<'a, T>[src]
impl<T: Hash> Hash for Option<T>[src]
fn hash<__HT: Hasher>(&self, state: &mut __HT)[src]
fn hash_slice<H: Hasher>(data: &[Self], state: &mut H) where
Self: Sized, 1.3.0[src]
Self: Sized,
Feeds a slice of this type into the given [Hasher]. Read more
impl<T: Debug> Debug for Option<T>[src]
Auto Trait Implementations
Blanket Implementations
impl<T, U> Into for T where
U: From<T>, [src]
U: From<T>,
impl<T> From for T[src]
impl<T, U> TryInto for T where
U: TryFrom<T>, [src]
U: TryFrom<T>,
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
fn try_into(Self) -> Result<U, <U as TryFrom<T>>::Error>[src]
impl<T, U> TryFrom for T where
U: Into<T>, [src]
U: Into<T>,
type Error = Infallible
The type returned in the event of a conversion error.
fn try_from(U) -> Result<T, <T as TryFrom<U>>::Error>[src]
impl<T> Borrow for T where
T: ?Sized, [src]
T: ?Sized,
impl<T> BorrowMut for T where
T: ?Sized, [src]
T: ?Sized,
fn borrow_mut(&mut Self) -> &mut T[src]
impl<T> Any for T where
T: 'static + ?Sized, [src]
T: 'static + ?Sized,