pub enum Option<T> {
None,
Some(T),
}
Expand description
The Option
type. See the module level documentation for more.
Variants§
Implementations§
source§impl<T> Option<T>
impl<T> Option<T>
1.70.0 · 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
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
Calculates the length of an Option<String>
as an Option<usize>
without moving the String
. 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:?}");
Run1.33.0 (const: unstable) · sourcepub fn as_pin_mut(self: Pin<&mut Option<T>>) -> Option<Pin<&mut T>>
pub fn as_pin_mut(self: Pin<&mut Option<T>>) -> Option<Pin<&mut T>>
1.75.0 · sourcepub fn as_slice(&self) -> &[T]
pub fn as_slice(&self) -> &[T]
Returns a slice of the contained value, if any. If this is None
, an
empty slice is returned. This can be useful to have a single type of
iterator over an Option
or slice.
Note: Should you have an Option<&T>
and wish to get a slice of T
,
you can unpack it via opt.map_or(&[], std::slice::from_ref)
.
§Examples
assert_eq!(
[Some(1234).as_slice(), None.as_slice()],
[&[1234][..], &[][..]],
);
RunThe inverse of this function is (discounting
borrowing) [_]::first
:
for i in [Some(1234_u16), None] {
assert_eq!(i.as_ref(), i.as_slice().first());
}
Run1.75.0 · sourcepub fn as_mut_slice(&mut self) -> &mut [T]
pub fn as_mut_slice(&mut self) -> &mut [T]
Returns a mutable slice of the contained value, if any. If this is
None
, an empty slice is returned. This can be useful to have a
single type of iterator over an Option
or slice.
Note: Should you have an Option<&mut T>
instead of a
&mut Option<T>
, which this method takes, you can obtain a mutable
slice via opt.map_or(&mut [], std::slice::from_mut)
.
§Examples
assert_eq!(
[Some(1234).as_mut_slice(), None.as_mut_slice()],
[&mut [1234][..], &mut [][..]],
);
RunThe result is a mutable slice of zero or one items that points into
our original Option
:
let mut x = Some(1234);
x.as_mut_slice()[0] += 1;
assert_eq!(x, Some(1235));
RunThe inverse of this method (discounting borrowing)
is [_]::first_mut
:
assert_eq!(Some(123).as_mut_slice().first_mut(), Some(&mut 123))
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");
Run§Recommended Message Style
We recommend that expect
messages are used to describe the reason you
expect the Option
should be Some
.
Hint: 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");
Runsourcepub 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");
Runsourcepub fn unwrap_or_else<F>(self, f: F) -> Twhere
F: FnOnce() -> T,
pub fn unwrap_or_else<F>(self, f: F) -> Twhere
F: FnOnce() -> T,
sourcepub fn unwrap_or_default(self) -> Twhere
T: Default,
pub fn unwrap_or_default(self) -> Twhere
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
let x: Option<u32> = None;
let y: Option<u32> = Some(12);
assert_eq!(x.unwrap_or_default(), 0);
assert_eq!(y.unwrap_or_default(), 12);
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!
Runsourcepub 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 (if Some
) or returns None
(if None
).
§Examples
Calculates the length of an Option<String>
as 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));
let x: Option<&str> = None;
assert_eq!(x.map(|s| s.len()), None);
Runsourcepub fn map_or<U, F>(self, default: U, f: F) -> Uwhere
F: FnOnce(T) -> U,
pub fn map_or<U, F>(self, default: U, f: F) -> Uwhere
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);
Runsourcepub fn map_or_else<U, D, F>(self, default: D, f: F) -> U
pub fn map_or_else<U, D, F>(self, default: D, f: F) -> U
Computes a default function result (if none), or applies a different function to the contained value (if any).
§Basic 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§Handling a Result-based fallback
A somewhat common occurrence when dealing with optional values
in combination with Result<T, E>
is the case where one wants to invoke
a fallible fallback if the option is not present. This example
parses a command line argument (if present), or the contents of a file to
an integer. However, unlike accessing the command line argument, reading
the file is fallible, so it must be wrapped with Ok
.
let v: u64 = std::env::args()
.nth(1)
.map_or_else(|| std::fs::read_to_string("/etc/someconfig.conf"), Ok)?
.parse()?;
Runsourcepub 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));
Runsourcepub 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 · sourcepub fn as_deref(&self) -> Option<&<T as Deref>::Target>where
T: Deref,
pub fn as_deref(&self) -> Option<&<T as Deref>::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 · sourcepub fn as_deref_mut(&mut self) -> Option<&mut <T as Deref>::Target>where
T: DerefMut,
pub fn as_deref_mut(&mut self) -> Option<&mut <T as Deref>::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()));
Runsourcepub 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
.
Arguments passed to and
are eagerly evaluated; if you are passing the
result of a function call, it is recommended to use and_then
, which is
lazily evaluated.
§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);
Runsourcepub fn and_then<U, F>(self, f: F) -> Option<U>
pub fn and_then<U, F>(self, f: F) -> 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 · sourcepub fn filter<P>(self, predicate: P) -> Option<T>
pub fn filter<P>(self, predicate: P) -> Option<T>
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));
Runsourcepub 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);
Runsourcepub fn or_else<F>(self, f: F) -> Option<T>
pub fn or_else<F>(self, f: F) -> 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 · 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 · 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 · 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));
Runsourcepub fn get_or_insert_default(&mut self) -> &mut Twhere
T: Default,
🔬This is a nightly-only experimental API. (option_get_or_insert_default
#82901)
pub fn get_or_insert_default(&mut self) -> &mut Twhere
T: Default,
option_get_or_insert_default
#82901)1.20.0 · sourcepub fn get_or_insert_with<F>(&mut self, f: F) -> &mut Twhere
F: FnOnce() -> T,
pub fn get_or_insert_with<F>(&mut self, f: F) -> &mut Twhere
F: FnOnce() -> T,
sourcepub fn take_if<P>(&mut self, predicate: P) -> Option<T>
🔬This is a nightly-only experimental API. (option_take_if
#98934)
pub fn take_if<P>(&mut self, predicate: P) -> Option<T>
option_take_if
#98934)Takes the value out of the option, but only if the predicate evaluates to
true
on a mutable reference to the value.
In other words, replaces self
with None
if the predicate returns true
.
This method operates similar to Option::take
but conditional.
§Examples
#![feature(option_take_if)]
let mut x = Some(42);
let prev = x.take_if(|v| if *v == 42 {
*v += 1;
false
} else {
false
});
assert_eq!(x, Some(43));
assert_eq!(prev, None);
let prev = x.take_if(|v| *v == 43);
assert_eq!(x, None);
assert_eq!(prev, Some(43));
Run1.31.0 (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);
Runsourcepub fn zip_with<U, F, R>(self, other: Option<U>, f: F) -> Option<R>where
F: FnOnce(T, U) -> R,
🔬This is a nightly-only experimental API. (option_zip
#70086)
pub fn zip_with<U, F, R>(self, other: Option<U>, f: F) -> Option<R>where
F: FnOnce(T, U) -> R,
option_zip
#70086)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);
Runsource§impl<T, U> Option<(T, U)>
impl<T, U> Option<(T, U)>
1.66.0 · sourcepub fn unzip(self) -> (Option<T>, Option<U>)
pub 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
let x = Some((1, "hi"));
let y = None::<(u8, u32)>;
assert_eq!(x.unzip(), (Some(1), Some("hi")));
assert_eq!(y.unzip(), (None, None));
Runsource§impl<T> Option<&T>
impl<T> Option<&T>
source§impl<T> Option<&mut T>
impl<T> Option<&mut T>
source§impl<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());
Runsource§impl<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 · source§impl<'a, T> From<&'a Option<T>> for Option<&'a T>
impl<'a, T> From<&'a Option<T>> for Option<&'a T>
source§fn 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 · source§impl<'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>
source§impl<A, V> FromIterator<Option<A>> for Option<V>where
V: FromIterator<A>,
impl<A, V> FromIterator<Option<A>> for Option<V>where
V: FromIterator<A>,
source§fn from_iter<I>(iter: I) -> Option<V>where
I: IntoIterator<Item = Option<A>>,
fn from_iter<I>(iter: I) -> Option<V>where
I: IntoIterator<Item = Option<A>>,
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.
source§impl<T> FromResidual for Option<T>
impl<T> FromResidual for Option<T>
source§fn from_residual(residual: Option<Infallible>) -> Option<T>
fn from_residual(residual: Option<Infallible>) -> Option<T>
try_trait_v2
#84277)Residual
type. Read more1.4.0 · source§impl<'a, T> IntoIterator for &'a Option<T>
impl<'a, T> IntoIterator for &'a Option<T>
1.4.0 · source§impl<'a, T> IntoIterator for &'a mut Option<T>
impl<'a, T> IntoIterator for &'a mut Option<T>
source§impl<T> Ord for Option<T>where
T: Ord,
impl<T> Ord for Option<T>where
T: Ord,
source§impl<T> PartialOrd for Option<T>where
T: PartialOrd,
impl<T> PartialOrd for Option<T>where
T: PartialOrd,
1.37.0 · source§impl<T, U> Product<Option<U>> for Option<T>where
T: Product<U>,
impl<T, U> Product<Option<U>> for Option<T>where
T: Product<U>,
source§fn product<I>(iter: I) -> Option<T>
fn product<I>(iter: I) -> Option<T>
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.
§Examples
This multiplies each number in a vector of strings,
if a string could not be parsed the operation returns None
:
let nums = vec!["5", "10", "1", "2"];
let total: Option<usize> = nums.iter().map(|w| w.parse::<usize>().ok()).product();
assert_eq!(total, Some(100));
let nums = vec!["5", "10", "one", "2"];
let total: Option<usize> = nums.iter().map(|w| w.parse::<usize>().ok()).product();
assert_eq!(total, None);
Runsource§impl<T> Residual<T> for Option<Infallible>
impl<T> Residual<T> for Option<Infallible>
1.37.0 · source§impl<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>,
source§fn sum<I>(iter: I) -> Option<T>
fn sum<I>(iter: I) -> Option<T>
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));
let words = vec!["have", "a", "good", "day"];
let total: Option<usize> = words.iter().map(|w| w.find('a')).sum();
assert_eq!(total, None);
Runsource§impl<T> Try for Option<T>
impl<T> Try for Option<T>
§type Output = T
type Output = T
try_trait_v2
#84277)?
when not short-circuiting.§type Residual = Option<Infallible>
type Residual = Option<Infallible>
try_trait_v2
#84277)FromResidual::from_residual
as part of ?
when short-circuiting. Read moresource§fn from_output(output: <Option<T> as Try>::Output) -> Option<T>
fn from_output(output: <Option<T> as Try>::Output) -> Option<T>
try_trait_v2
#84277)Output
type. Read moresource§fn branch(
self
) -> ControlFlow<<Option<T> as Try>::Residual, <Option<T> as Try>::Output>
fn branch( self ) -> ControlFlow<<Option<T> as Try>::Residual, <Option<T> as Try>::Output>
try_trait_v2
#84277)?
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