pub enum Option<T> {
None,
Some(T),
}
Expand description
The Option
type. See the module level documentation for more.
Variants
None
No value.
Some(T)
Some value of type T
.
Implementations
sourceimpl<T> Option<T>
impl<T> Option<T>
sourcepub fn is_some_and(&self, f: impl FnOnce(&T) -> bool) -> bool
pub fn is_some_and(&self, f: impl FnOnce(&T) -> bool) -> bool
Returns true
if the option is a Some
and the value inside of it matches a predicate.
Examples
#![feature(is_some_with)]
let x: Option<u32> = Some(2);
assert_eq!(x.is_some_and(|&x| x > 1), true);
let x: Option<u32> = Some(0);
assert_eq!(x.is_some_and(|&x| x > 1), false);
let x: Option<u32> = None;
assert_eq!(x.is_some_and(|&x| x > 1), false);
Runconst: 1.48.0 · sourcepub const fn as_ref(&self) -> Option<&T>
pub const fn as_ref(&self) -> Option<&T>
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:?}");
Runconst: unstable · sourcepub fn expect(self, msg: &str) -> T
pub fn expect(self, msg: &str) -> T
Returns the contained Some
value, consuming the self
value.
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("fruits are healthy"), "value");
Runlet x: Option<&str> = None;
x.expect("fruits are healthy"); // panics with `fruits are healthy`
RunRecommended Message Style
We recommend that expect
messages are used to describe the reason you
expect the Option
should be Some
.
let item = slice.get(0)
.expect("slice should not be empty");
RunHint: If you’re having trouble remembering how to phrase expect error messages remember to focus on the word “should” as in “env variable should be set by blah” or “the given binary should be available and executable by the current user”.
For more detail on expect message styles and the reasoning behind our
recommendation please refer to the section on “Common Message
Styles” in the std::error
module docs.
const: unstable · sourcepub fn unwrap(self) -> T
pub fn unwrap(self) -> T
Returns the contained Some
value, consuming the self
value.
Because this function may panic, its use is generally discouraged.
Instead, prefer to use pattern matching and handle the None
case explicitly, or call unwrap_or
, unwrap_or_else
, or
unwrap_or_default
.
Panics
Panics if the self value equals None
.
Examples
let x = Some("air");
assert_eq!(x.unwrap(), "air");
Runlet x: Option<&str> = None;
assert_eq!(x.unwrap(), "air"); // fails
Runconst: unstable · sourcepub fn unwrap_or(self, default: T) -> T
pub fn unwrap_or(self, default: T) -> T
Returns the contained Some
value or a provided 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");
Runconst: unstable · sourcepub fn unwrap_or_else<F>(self, f: F) -> T where
F: FnOnce() -> T,
pub fn unwrap_or_else<F>(self, f: F) -> T where
F: FnOnce() -> T,
const: unstable · sourcepub fn unwrap_or_default(self) -> T where
T: Default,
pub fn unwrap_or_default(self) -> T where
T: Default,
Returns the contained Some
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);
Run1.58.0 (const: unstable) · sourcepub unsafe fn unwrap_unchecked(self) -> T
pub unsafe fn unwrap_unchecked(self) -> T
Returns the contained Some
value, consuming the self
value,
without checking that the value is not None
.
Safety
Calling this method on None
is undefined behavior.
Examples
let x = Some("air");
assert_eq!(unsafe { x.unwrap_unchecked() }, "air");
Runlet x: Option<&str> = None;
assert_eq!(unsafe { x.unwrap_unchecked() }, "air"); // Undefined behavior!
Runconst: unstable · sourcepub fn map<U, F>(self, f: F) -> Option<U> where
F: FnOnce(T) -> U,
pub fn map<U, F>(self, f: F) -> Option<U> where
F: FnOnce(T) -> U,
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));
Runconst: unstable · sourcepub fn inspect<F>(self, f: F) -> Self where
F: FnOnce(&T),
pub fn inspect<F>(self, f: F) -> Self where
F: FnOnce(&T),
Calls the provided closure with a reference to the contained value (if Some
).
Examples
#![feature(result_option_inspect)]
let v = vec![1, 2, 3, 4, 5];
// prints "got: 4"
let x: Option<&usize> = v.get(3).inspect(|x| println!("got: {x}"));
// prints nothing
let x: Option<&usize> = v.get(5).inspect(|x| println!("got: {x}"));
Runconst: unstable · sourcepub fn map_or<U, F>(self, default: U, f: F) -> U where
F: FnOnce(T) -> U,
pub fn map_or<U, F>(self, default: U, f: F) -> U where
F: FnOnce(T) -> U,
Returns the provided default result (if none), or applies a function to the contained value (if any).
Arguments passed to map_or
are eagerly evaluated; if you are passing
the result of a function call, it is recommended to use map_or_else
,
which is lazily evaluated.
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);
Runconst: unstable · sourcepub fn map_or_else<U, D, F>(self, default: D, f: F) -> U where
D: FnOnce() -> U,
F: FnOnce(T) -> U,
pub fn map_or_else<U, D, F>(self, default: D, f: F) -> U where
D: FnOnce() -> U,
F: FnOnce(T) -> U,
const: unstable · sourcepub fn ok_or<E>(self, err: E) -> Result<T, E>
pub fn ok_or<E>(self, err: E) -> Result<T, E>
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));
Runconst: unstable · sourcepub fn ok_or_else<E, F>(self, err: F) -> Result<T, E> where
F: FnOnce() -> E,
pub fn ok_or_else<E, F>(self, err: F) -> Result<T, E> where
F: FnOnce() -> E,
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));
Run1.40.0 (const: unstable) · sourcepub fn as_deref(&self) -> Option<&T::Target> where
T: Deref,
pub fn as_deref(&self) -> Option<&T::Target> where
T: Deref,
Converts from Option<T>
(or &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
.
Examples
let x: Option<String> = Some("hey".to_owned());
assert_eq!(x.as_deref(), Some("hey"));
let x: Option<String> = None;
assert_eq!(x.as_deref(), None);
Run1.40.0 (const: unstable) · sourcepub fn as_deref_mut(&mut self) -> Option<&mut T::Target> where
T: DerefMut,
pub fn as_deref_mut(&mut self) -> Option<&mut T::Target> where
T: DerefMut,
Converts from Option<T>
(or &mut Option<T>
) to Option<&mut T::Target>
.
Leaves the original Option
in-place, creating a new one containing a mutable reference to
the inner type’s Deref::Target
type.
Examples
let mut x: Option<String> = Some("hey".to_owned());
assert_eq!(x.as_deref_mut().map(|x| {
x.make_ascii_uppercase();
x
}), Some("HEY".to_owned().as_mut_str()));
Runconst: unstable · sourcepub fn iter(&self) -> Iter<'_, T>ⓘNotable traits for Iter<'a, A>impl<'a, A> Iterator for Iter<'a, A> type Item = &'a A;
pub fn iter(&self) -> Iter<'_, T>ⓘNotable traits for Iter<'a, A>impl<'a, A> Iterator for Iter<'a, A> type Item = &'a A;
sourcepub fn iter_mut(&mut self) -> IterMut<'_, T>ⓘNotable traits for IterMut<'a, A>impl<'a, A> Iterator for IterMut<'a, A> type Item = &'a mut A;
pub fn iter_mut(&mut self) -> IterMut<'_, T>ⓘNotable traits for IterMut<'a, A>impl<'a, A> Iterator for IterMut<'a, A> type Item = &'a mut A;
const: unstable · sourcepub fn and<U>(self, optb: Option<U>) -> Option<U>
pub fn and<U>(self, optb: Option<U>) -> Option<U>
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);
Runconst: unstable · sourcepub fn and_then<U, F>(self, f: F) -> Option<U> where
F: FnOnce(T) -> Option<U>,
pub fn and_then<U, F>(self, f: F) -> Option<U> where
F: FnOnce(T) -> Option<U>,
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_then_to_string(x: u32) -> Option<String> {
x.checked_mul(x).map(|sq| sq.to_string())
}
assert_eq!(Some(2).and_then(sq_then_to_string), Some(4.to_string()));
assert_eq!(Some(1_000_000).and_then(sq_then_to_string), None); // overflowed!
assert_eq!(None.and_then(sq_then_to_string), None);
RunOften used to chain fallible operations that may return None
.
let arr_2d = [["A0", "A1"], ["B0", "B1"]];
let item_0_1 = arr_2d.get(0).and_then(|row| row.get(1));
assert_eq!(item_0_1, Some(&"A1"));
let item_2_0 = arr_2d.get(2).and_then(|row| row.get(0));
assert_eq!(item_2_0, None);
Run1.27.0 (const: unstable) · sourcepub fn filter<P>(self, predicate: P) -> Self where
P: FnOnce(&T) -> bool,
pub fn filter<P>(self, predicate: P) -> Self where
P: FnOnce(&T) -> bool,
Returns None
if the option is None
, otherwise calls predicate
with the wrapped value and returns:
Some(t)
ifpredicate
returnstrue
(wheret
is the wrapped value), andNone
ifpredicate
returnsfalse
.
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));
Runconst: unstable · sourcepub fn or(self, optb: Option<T>) -> Option<T>
pub fn or(self, optb: Option<T>) -> Option<T>
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);
Runconst: unstable · sourcepub fn or_else<F>(self, f: F) -> Option<T> where
F: FnOnce() -> Option<T>,
pub fn or_else<F>(self, f: F) -> Option<T> where
F: FnOnce() -> Option<T>,
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);
Run1.37.0 (const: unstable) · sourcepub fn xor(self, optb: Option<T>) -> Option<T>
pub fn xor(self, optb: Option<T>) -> Option<T>
Returns Some
if exactly one of self
, optb
is Some
, otherwise returns None
.
Examples
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);
Run1.53.0 (const: unstable) · sourcepub fn insert(&mut self, value: T) -> &mut T
pub fn insert(&mut self, value: T) -> &mut T
Inserts value
into the option, then returns a mutable reference to it.
If the option already contains a value, the old value is dropped.
See also Option::get_or_insert
, which doesn’t update the value if
the option already contains Some
.
Example
let mut opt = None;
let val = opt.insert(1);
assert_eq!(*val, 1);
assert_eq!(opt.unwrap(), 1);
let val = opt.insert(2);
assert_eq!(*val, 2);
*val = 3;
assert_eq!(opt.unwrap(), 3);
Run1.20.0 (const: unstable) · sourcepub fn get_or_insert(&mut self, value: T) -> &mut T
pub fn get_or_insert(&mut self, value: T) -> &mut T
Inserts value
into the option if it is None
, then
returns a mutable reference to the contained value.
See also Option::insert
, which updates the value even if
the option already contains Some
.
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));
Runconst: unstable · sourcepub fn get_or_insert_default(&mut self) -> &mut T where
T: Default,
pub fn get_or_insert_default(&mut self) -> &mut T where
T: Default,
1.20.0 (const: unstable) · sourcepub fn get_or_insert_with<F>(&mut self, f: F) -> &mut T where
F: FnOnce() -> T,
pub fn get_or_insert_with<F>(&mut self, f: F) -> &mut T where
F: FnOnce() -> T,
1.31.0 (const: unstable) · sourcepub fn replace(&mut self, value: T) -> Option<T>
pub fn replace(&mut self, value: T) -> Option<T>
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);
Runconst: unstable · sourcepub fn contains<U>(&self, x: &U) -> bool where
U: PartialEq<T>,
pub fn contains<U>(&self, x: &U) -> bool where
U: PartialEq<T>,
Returns true
if the option is a Some
value containing the given value.
Examples
#![feature(option_result_contains)]
let x: Option<u32> = Some(2);
assert_eq!(x.contains(&2), true);
let x: Option<u32> = Some(3);
assert_eq!(x.contains(&2), false);
let x: Option<u32> = None;
assert_eq!(x.contains(&2), false);
Runconst: unstable · sourcepub fn zip_with<U, F, R>(self, other: Option<U>, f: F) -> Option<R> where
F: FnOnce(T, U) -> R,
pub fn zip_with<U, F, R>(self, other: Option<U>, f: F) -> Option<R> where
F: FnOnce(T, U) -> R,
Zips self
and another Option
with function f
.
If self
is Some(s)
and other
is Some(o)
, this method returns Some(f(s, o))
.
Otherwise, None
is returned.
Examples
#![feature(option_zip)]
#[derive(Debug, PartialEq)]
struct Point {
x: f64,
y: f64,
}
impl Point {
fn new(x: f64, y: f64) -> Self {
Self { x, y }
}
}
let x = Some(17.5);
let y = Some(42.7);
assert_eq!(x.zip_with(y, Point::new), Some(Point { x: 17.5, y: 42.7 }));
assert_eq!(x.zip_with(None, Point::new), None);
Runsourceimpl<T, U> Option<(T, U)>
impl<T, U> Option<(T, U)>
sourcepub const fn unzip(self) -> (Option<T>, Option<U>)
pub const fn unzip(self) -> (Option<T>, Option<U>)
Unzips an option containing a tuple of two options.
If self
is Some((a, b))
this method returns (Some(a), Some(b))
.
Otherwise, (None, None)
is returned.
Examples
#![feature(unzip_option)]
let x = Some((1, "hi"));
let y = None::<(u8, u32)>;
assert_eq!(x.unzip(), (Some(1), Some("hi")));
assert_eq!(y.unzip(), (None, None));
Runsourceimpl<T> Option<&T>
impl<T> Option<&T>
sourceimpl<T> Option<&mut T>
impl<T> Option<&mut T>
sourceimpl<T, E> Option<Result<T, E>>
impl<T, E> Option<Result<T, E>>
1.33.0 (const: unstable) · sourcepub fn transpose(self) -> Result<Option<T>, E>
pub fn transpose(self) -> Result<Option<T>, E>
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());
Runsourceimpl<T> Option<Option<T>>
impl<T> Option<Option<T>>
1.40.0 (const: unstable) · sourcepub fn flatten(self) -> Option<T>
pub fn flatten(self) -> Option<T>
Converts from Option<Option<T>>
to Option<T>
.
Examples
Basic usage:
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());
RunFlattening only removes one level of nesting at a time:
let x: Option<Option<Option<u32>>> = Some(Some(Some(6)));
assert_eq!(Some(Some(6)), x.flatten());
assert_eq!(Some(6), x.flatten().flatten());
RunTrait Implementations
1.30.0 (const: unstable) · sourceimpl<'a, T> From<&'a Option<T>> for Option<&'a T>
impl<'a, T> From<&'a Option<T>> for Option<&'a T>
const: unstable · sourcefn from(o: &'a Option<T>) -> Option<&'a T>
fn from(o: &'a Option<T>) -> Option<&'a T>
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 from
to first take an Option
to a reference
to the value inside the original.
let s: Option<String> = Some(String::from("Hello, Rustaceans!"));
let o: Option<usize> = Option::from(&s).map(|ss: &String| ss.len());
println!("Can still print s: {s:?}");
assert_eq!(o, Some(18));
Run1.30.0 (const: unstable) · sourceimpl<'a, T> From<&'a mut Option<T>> for Option<&'a mut T>
impl<'a, T> From<&'a mut Option<T>> for Option<&'a mut T>
sourceimpl<A, V: FromIterator<A>> FromIterator<Option<A>> for Option<V>
impl<A, V: FromIterator<A>> FromIterator<Option<A>> for Option<V>
sourcefn from_iter<I: IntoIterator<Item = Option<A>>>(iter: I) -> Option<V>
fn from_iter<I: IntoIterator<Item = Option<A>>>(iter: I) -> Option<V>
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 of type
V
containing the values of each Option
is returned.
Examples
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]));
RunAs 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);
RunSince 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);
RunSince the third element caused an underflow, no further elements were taken,
so the final value of shared
is 6 (= 3 + 2 + 1
), not 16.
const: unstable · sourceimpl<T> FromResidual<<Option<T> as Try>::Residual> for Option<T>
impl<T> FromResidual<<Option<T> as Try>::Residual> for Option<T>
const: unstable · sourcefn from_residual(residual: Option<Infallible>) -> Self
fn from_residual(residual: Option<Infallible>) -> Self
Constructs the type from a compatible Residual
type. Read more
sourceimpl<T> FromResidual<Yeet<()>> for Option<T>
impl<T> FromResidual<Yeet<()>> for Option<T>
sourceimpl<T> IntoIterator for Option<T>
impl<T> IntoIterator for Option<T>
1.4.0 · sourceimpl<'a, T> IntoIterator for &'a Option<T>
impl<'a, T> IntoIterator for &'a Option<T>
1.4.0 · sourceimpl<'a, T> IntoIterator for &'a mut Option<T>
impl<'a, T> IntoIterator for &'a mut Option<T>
sourceimpl<T: Ord> Ord for Option<T>
impl<T: Ord> Ord for Option<T>
1.21.0 · sourcefn max(self, other: Self) -> Self where
Self: Sized,
fn max(self, other: Self) -> Self where
Self: Sized,
Compares and returns the maximum of two values. Read more
sourceimpl<T: PartialOrd> PartialOrd<Option<T>> for Option<T>
impl<T: PartialOrd> PartialOrd<Option<T>> for Option<T>
sourcefn partial_cmp(&self, other: &Option<T>) -> Option<Ordering>
fn partial_cmp(&self, other: &Option<T>) -> Option<Ordering>
This method returns an ordering between self
and other
values if one exists. Read more
sourcefn lt(&self, other: &Rhs) -> bool
fn lt(&self, other: &Rhs) -> bool
This method tests less than (for self
and other
) and is used by the <
operator. Read more
sourcefn le(&self, other: &Rhs) -> bool
fn le(&self, other: &Rhs) -> bool
This method tests less than or equal to (for self
and other
) and is used by the <=
operator. Read more
sourceimpl<T> Residual<T> for Option<Infallible>
impl<T> Residual<T> for Option<Infallible>
1.37.0 · sourceimpl<T, U> Sum<Option<U>> for Option<T> where
T: Sum<U>,
impl<T, U> Sum<Option<U>> for Option<T> where
T: Sum<U>,
sourcefn sum<I>(iter: I) -> Option<T> where
I: Iterator<Item = Option<U>>,
fn sum<I>(iter: I) -> Option<T> where
I: Iterator<Item = Option<U>>,
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.
Examples
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
:
let words = vec!["have", "a", "great", "day"];
let total: Option<usize> = words.iter().map(|w| w.find('a')).sum();
assert_eq!(total, Some(5));
Runconst: unstable · sourceimpl<T> Try for Option<T>
impl<T> Try for Option<T>
type Residual = Option<Infallible>
type Residual = Option<Infallible>
The type of the value passed to FromResidual::from_residual
as part of ?
when short-circuiting. Read more
const: unstable · sourcefn from_output(output: Self::Output) -> Self
fn from_output(output: Self::Output) -> Self
Constructs the type from its Output
type. Read more
const: unstable · sourcefn branch(self) -> ControlFlow<Self::Residual, Self::Output>
fn branch(self) -> ControlFlow<Self::Residual, Self::Output>
Used in ?
to decide whether the operator should produce a value
(because this returned ControlFlow::Continue
)
or propagate a value back to the caller
(because this returned ControlFlow::Break
). Read more
impl<T: Copy> Copy for Option<T>
impl<T: Eq> Eq for Option<T>
impl<T> StructuralEq for Option<T>
impl<T> StructuralPartialEq for Option<T>
Auto Trait Implementations
impl<T> RefUnwindSafe for Option<T> where
T: RefUnwindSafe,
impl<T> Send for Option<T> where
T: Send,
impl<T> Sync for Option<T> where
T: Sync,
impl<T> Unpin for Option<T> where
T: Unpin,
impl<T> UnwindSafe for Option<T> where
T: UnwindSafe,
Blanket Implementations
sourceimpl<T> BorrowMut<T> for T where
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more