pub enum Option<T> { None, Some(T), }
The Option
type. See the module level documentation for more.
None
No value
Some(T)
Some value T
impl<T> Option<T>
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pub fn is_some(&self) -> bool
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Returns true
if the option is a Some
value.
pub fn is_none(&self) -> bool
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Returns true
if the option is a None
value.
pub fn as_ref(&self) -> Option<&T>
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Converts from &Option<T>
to Option<&T>
.
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);
pub fn as_mut(&mut self) -> Option<&mut T>
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Converts from &mut Option<T>
to Option<&mut T>
.
pub fn as_pin_ref(self: Pin<&'a Option<T>>) -> Option<Pin<&'a T>>
[src]1.33.0
Converts from Pin<&Option<T>>
to Option<Pin<&T>>
pub fn as_pin_mut(self: Pin<&'a mut Option<T>>) -> Option<Pin<&'a mut T>>
[src]1.33.0
Converts from Pin<&mut Option<T>>
to Option<Pin<&mut T>>
pub fn expect(self, msg: &str) -> T
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Unwraps an option, yielding the content of a Some
.
Panics if the value is a None
with a custom panic message provided by msg
.
pub fn unwrap(self) -> T
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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 if the self value equals None
.
pub fn unwrap_or(self, def: T) -> T
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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.
pub fn unwrap_or_else<F>(self, f: F) -> T where
F: FnOnce() -> T,
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Returns the contained value or computes it from a closure.
pub fn map<U, F>(self, f: F) -> Option<U> where
F: FnOnce(T) -> U,
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Maps an Option<T>
to Option<U>
by applying a function to a contained value.
Converts an Option<
String
>
into an Option<
usize
>
, consuming the original:
pub fn map_or<U, F>(self, default: U, f: F) -> U where
F: FnOnce(T) -> U,
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Applies a function to the contained value (if any), or returns the provided default (if not).
pub fn map_or_else<U, D, F>(self, default: D, f: F) -> U where
D: FnOnce() -> U,
F: FnOnce(T) -> U,
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Applies a function to the contained value (if any), or computes a default (if not).
pub fn ok_or<E>(self, err: E) -> Result<T, E>
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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.
pub fn ok_or_else<E, F>(self, err: F) -> Result<T, E> where
F: FnOnce() -> E,
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Transforms the Option<T>
into a Result<T, E>
, mapping Some(v)
to Ok(v)
and None
to Err(err())
.
pub fn iter(&self) -> Iter<T>
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impl<'a, A> Iterator for Iter<'a, A> type Item = &'a A;
Returns an iterator over the possibly contained value.
pub fn iter_mut(&mut self) -> IterMut<T>
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impl<'a, A> Iterator for IterMut<'a, A> type Item = &'a mut A;
Returns a mutable iterator over the possibly contained value.
pub fn and<U>(self, optb: Option<U>) -> Option<U>
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Returns None
if the option is None
, otherwise returns optb
.
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);
pub fn and_then<U, F>(self, f: F) -> Option<U> where
F: FnOnce(T) -> Option<U>,
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Returns None
if the option is None
, otherwise calls f
with the wrapped value and returns the result.
Some languages call this operation flatmap.
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);
pub fn filter<P>(self, predicate: P) -> Option<T> where
P: FnOnce(&T) -> bool,
[src]1.27.0
Returns None
if the option is None
, otherwise calls predicate
with the wrapped value and returns:
Some(t)
if predicate
returns true
(where t
is the wrapped value), andNone
if predicate
returns false
.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.
pub fn or(self, optb: Option<T>) -> Option<T>
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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.
pub fn or_else<F>(self, f: F) -> Option<T> where
F: FnOnce() -> Option<T>,
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Returns the option if it contains a value, otherwise calls f
and returns the result.
pub fn xor(self, optb: Option<T>) -> Option<T>
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pub fn get_or_insert(&mut self, v: T) -> &mut T
[src]1.20.0
impl<'_, F> Future for &'_ mut F where F: Unpin + Future + ?Sized, type Output = <F as Future>::Output; impl<'_, I> Iterator for &'_ mut I where I: Iterator + ?Sized, type Item = <I as Iterator>::Item; impl<'_, R: Read + ?Sized> Read for &'_ mut R impl<'_, W: Write + ?Sized> Write for &'_ mut W
Inserts v
into the option if it is None
, then returns a mutable reference to the contained value.
pub fn get_or_insert_with<F>(&mut self, f: F) -> &mut T where
F: FnOnce() -> T,
[src]1.20.0
impl<'_, F> Future for &'_ mut F where F: Unpin + Future + ?Sized, type Output = <F as Future>::Output; impl<'_, I> Iterator for &'_ mut I where I: Iterator + ?Sized, type Item = <I as Iterator>::Item; impl<'_, R: Read + ?Sized> Read for &'_ mut R impl<'_, W: Write + ?Sized> Write for &'_ mut W
Inserts a value computed from f
into the option if it is None
, then returns a mutable reference to the contained value.
pub fn take(&mut self) -> Option<T>
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Takes the value out of the option, leaving a None
in its place.
pub fn replace(&mut self, value: T) -> Option<T>
[src]1.31.0
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.
impl<'_, T> Option<&'_ T> where
T: Copy,
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pub fn copied(self) -> Option<T>
[src]1.35.0
Maps an Option<&T>
to an Option<T>
by copying the contents of the option.
impl<'_, T> Option<&'_ mut T> where
T: Copy,
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pub fn copied(self) -> Option<T>
[src]1.35.0
Maps an Option<&mut T>
to an Option<T>
by copying the contents of the option.
impl<'_, T> Option<&'_ T> where
T: Clone,
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pub fn cloned(self) -> Option<T>
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Maps an Option<&T>
to an Option<T>
by cloning the contents of the option.
impl<'_, T> Option<&'_ mut T> where
T: Clone,
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pub fn cloned(self) -> Option<T>
[src]1.26.0
Maps an Option<&mut T>
to an Option<T>
by cloning the contents of the option.
impl<T> Option<T> where
T: Default,
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pub fn unwrap_or_default(self) -> T
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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.
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.
impl<T> Option<T> where
T: Deref,
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pub fn deref(&self) -> Option<&<T as Deref>::Target>
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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>>
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pub fn transpose(self) -> Result<Option<T>, E>
[src]1.33.0
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(_)
.
impl<T> Option<Option<T>>
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pub fn flatten(self) -> Option<T>
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Converts from Option<Option<T>>
to Option<T>
Basic usage:
#![feature(option_flattening)] let x: Option<Option<u32>> = Some(Some(6)); assert_eq!(Some(6), x.flatten()); let x: Option<Option<u32>> = Some(None); assert_eq!(None, x.flatten()); let x: Option<Option<u32>> = None; assert_eq!(None, x.flatten());
Flattening once only removes one level of nesting:
impl<T, U> Sum<Option<U>> for Option<T> where
T: Sum<U>,
[src]1.37.0
fn sum<I>(iter: I) -> Option<T> where
I: Iterator<Item = Option<U>>,
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Takes each element in the Iterator
: if it is a None
, no further elements are taken, and the None
is returned. Should no None
occur, the sum of all elements is returned.
This sums up the position of the character 'a' in a vector of strings, if a word did not have the character 'a' the operation returns None
:
impl<T> Copy for Option<T> where
T: Copy,
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impl<T> Default for Option<T>
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impl<T> Hash for Option<T> where
T: Hash,
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fn hash<__HT>(&self, state: &mut __HT) where
__HT: Hasher,
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fn hash_slice<H>(data: &[Self], state: &mut H) where
H: Hasher,
[src]1.3.0
Feeds a slice of this type into the given [Hasher
]. Read more
impl<T> Clone for Option<T> where
T: Clone,
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impl<T> Eq for Option<T> where
T: Eq,
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impl<T> Try for Option<T>
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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>
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fn from_ok(v: T) -> Option<T>
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fn from_error(NoneError) -> Option<T>
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impl<T> PartialOrd<Option<T>> for Option<T> where
T: PartialOrd<T>,
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fn partial_cmp(&self, other: &Option<T>) -> Option<Ordering>
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fn lt(&self, other: &Option<T>) -> bool
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fn le(&self, other: &Option<T>) -> bool
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fn gt(&self, other: &Option<T>) -> bool
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fn ge(&self, other: &Option<T>) -> bool
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impl<T> IntoIterator for Option<T>
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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>
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impl<A> Iterator for IntoIter<A> type Item = A;
impl<'a, T> IntoIterator for &'a Option<T>
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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>
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impl<'a, A> Iterator for Iter<'a, A> type Item = &'a A;
impl<'a, T> IntoIterator for &'a mut Option<T>
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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>
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impl<'a, A> Iterator for IterMut<'a, A> type Item = &'a mut A;
impl<T> Ord for Option<T> where
T: Ord,
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fn cmp(&self, other: &Option<T>) -> Ordering
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fn max(self, other: Self) -> Self
[src]1.21.0
Compares and returns the maximum of two values. Read more
fn min(self, other: Self) -> Self
[src]1.21.0
Compares and returns the minimum of two values. Read more
fn clamp(self, min: Self, max: Self) -> Self
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Restrict a value to a certain interval. Read more
impl<T, U> Product<Option<U>> for Option<T> where
T: Product<U>,
[src]1.37.0
fn product<I>(iter: I) -> Option<T> where
I: Iterator<Item = Option<U>>,
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Takes each element in the Iterator
: if it is a None
, no further elements are taken, and the None
is returned. Should no None
occur, the product of all elements is returned.
impl<T> Debug for Option<T> where
T: Debug,
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impl<T> PartialEq<Option<T>> for Option<T> where
T: PartialEq<T>,
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impl<A, V> FromIterator<Option<A>> for Option<V> where
V: FromIterator<A>,
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fn from_iter<I>(iter: I) -> Option<V> where
I: IntoIterator<Item = Option<A>>,
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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.
Here is an example which increments every integer in a vector. We use the checked variant of add
that returns None
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]));
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);
Since the last element is zero, it would underflow. Thus, the resulting value is None
.
Here is a variation on the previous example, showing that no further elements are taken from iter
after the first None
.
let items = vec![3_u16, 2, 1, 10]; let mut shared = 0; let res: Option<Vec<u16>> = items .iter() .map(|x| { shared += x; x.checked_sub(2) }) .collect(); assert_eq!(res, None); assert_eq!(shared, 6);
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> From<T> for Option<T>
[src]1.12.0
impl<'a, T> From<&'a Option<T>> for Option<&'a T>
[src]1.30.0
impl<'a, T> From<&'a mut Option<T>> for Option<&'a mut T>
[src]1.30.0
impl<T> UnwindSafe for Option<T> where
T: UnwindSafe,
impl<T> RefUnwindSafe for Option<T> where
T: RefUnwindSafe,
impl<T> Unpin for Option<T> where
T: Unpin,
impl<T> Send for Option<T> where
T: Send,
impl<T> Sync for Option<T> where
T: Sync,
impl<T, U> TryFrom<U> for T where
U: Into<T>,
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type Error = Infallible
The type returned in the event of a conversion error.
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
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impl<I> IntoIterator for I where
I: Iterator,
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type Item = <I as Iterator>::Item
The type of the elements being iterated over.
type IntoIter = I
Which kind of iterator are we turning this into?
fn into_iter(self) -> I
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impl<T, U> Into<U> for T where
U: From<T>,
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impl<T> From<T> for T
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impl<T, U> TryInto<U> for T where
U: TryFrom<T>,
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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>
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impl<T> Borrow<T> for T where
T: ?Sized,
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fn borrow(&self) -> &T
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impl<'_, F> Future for &'_ mut F where F: Unpin + Future + ?Sized, type Output = <F as Future>::Output; impl<'_, I> Iterator for &'_ mut I where I: Iterator + ?Sized, type Item = <I as Iterator>::Item; impl<'_, R: Read + ?Sized> Read for &'_ mut R impl<'_, W: Write + ?Sized> Write for &'_ mut W
impl<T> BorrowMut<T> for T where
T: ?Sized,
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fn borrow_mut(&mut self) -> &mut T
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impl<'_, F> Future for &'_ mut F where F: Unpin + Future + ?Sized, type Output = <F as Future>::Output; impl<'_, I> Iterator for &'_ mut I where I: Iterator + ?Sized, type Item = <I as Iterator>::Item; impl<'_, R: Read + ?Sized> Read for &'_ mut R impl<'_, W: Write + ?Sized> Write for &'_ mut W
impl<T> Any for T where
T: 'static + ?Sized,
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impl<T> ToOwned for T where
T: Clone,
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© 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
https://doc.rust-lang.org/std/option/enum.Option.html