# 1.0.0[−][src]Enum std::option::Option

    pub enum Option<T> {
        None,
        Some(T),
    }

The `Option` type. See the module level documentation for more.

## Variants

`None`

No value

`Some(T)`

Some value `T`

## Implementations

### `impl<T> Option<T>`[src]

#### `#[must_use = "if you intended to assert that this has a value, consider `.unwrap()` instead"]pub const fn is_some(&self) -> bool` 1.0.0 (const: 1.48.0)[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

#### `#[must_use = "if you intended to assert that this doesn't have a value, consider \ `.and_then(|| panic!(\"`Option` had a value when expected `None`\"))` instead"]pub const fn is_none(&self) -> bool` 1.0.0 (const: 1.48.0)[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

#### `#[must_use]pub fn contains<U>(&self, x: &U) -> bool where
U: PartialEq<T>,` [src]

🔬 This is a nightly-only experimental API. (`option_result_contains` #62358)

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);

Run

#### `pub const fn as_ref(&self) -> Option<&T>`1.0.0 (const: 1.48.0)[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 `&mut 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(self: Pin<&Option<T>>) -> Option<Pin<&T>>`1.33.0[src]

Converts from `Pin``<&Option<T>>` to `Option<``Pin``<&T>>`.

#### `pub fn as_pin_mut(self: Pin<&mut Option<T>>) -> Option<Pin<&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]

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
ⓘ

    let x: Option<&str> = None;
    x.expect("fruits are healthy"); // panics with `fruits are healthy`

Run

#### `pub fn unwrap(self) -> T`[src]

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");

Run
ⓘ

    let x: Option<&str> = None;
    assert_eq!(x.unwrap(), "air"); // fails

Run

#### `pub fn unwrap_or(self, default: T) -> T`[src]

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");

Run

#### `pub fn unwrap_or_else<F>(self, f: F) -> T where
F: FnOnce() -> T,` [src]

Returns the contained `Some` 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>(self, f: F) -> Option<U> where
F: FnOnce(T) -> 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>(self, default: U, f: F) -> U where
F: FnOnce(T) -> U,` [src]

Applies a function to the contained value (if any), or returns the provided default (if not).

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);

Run

#### `pub fn map_or_else<U, D, F>(self, default: D, f: F) -> U where
F: FnOnce(T) -> U,
D: FnOnce() -> U,` [src]

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>(self, err: F) -> Result<T, E> where
F: FnOnce() -> 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

#### `pub fn insert(&mut self, value: T) -> &mut Tⓘ

### Notable traits for &'_ mut F

`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 Rimpl<W: Write + ?Sized> Write for &mut W`
`[src]

🔬 This is a nightly-only experimental API. (`option_insert` #78271)

newly added

Inserts `value` into the option then returns a mutable reference to it.

If the option already contains a value, the old value is dropped.

# Example

    #![feature(option_insert)]

    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);

Run

#### `pub fn iter(&self) -> Iter<'_, T>ⓘ

### Notable traits for Iter<'a, A>

`impl<'a, A> Iterator for Iter<'a, A> type Item = &'a A;`
`[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

#### `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;`
`[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>(self, f: F) -> Option<U> where
F: FnOnce(T) -> 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>(self, predicate: P) -> Option<T> where
P: FnOnce(&T) -> bool,` 1.27.0[src]

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), and
- `None` 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.

# 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>(self, f: F) -> Option<T> where
F: FnOnce() -> 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>`1.37.0[src]

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);

Run

#### `pub fn get_or_insert(&mut self, value: T) -> &mut Tⓘ

### Notable traits for &'_ mut F

`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 Rimpl<W: Write + ?Sized> Write for &mut W`
`1.20.0[src]

Inserts `value` 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>(&mut self, f: F) -> &mut Tⓘ

### Notable traits for &'_ mut F

`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 Rimpl<W: Write + ?Sized> Write for &mut W`
where
F: FnOnce() -> T,` 1.20.0[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

#### `pub fn zip<U>(self, other: Option<U>) -> Option<(T, U)>`1.46.0[src]

Zips `self` with another `Option`.

If `self` is `Some(s)` and `other` is `Some(o)`, this method returns `Some((s, o))`. Otherwise, `None` is returned.

# Examples

    let x = Some(1);
    let y = Some("hi");
    let z = None::<u8>;

    assert_eq!(x.zip(y), Some((1, "hi")));
    assert_eq!(x.zip(z), None);

Run

#### `pub fn zip_with<U, F, R>(self, other: Option<U>, f: F) -> Option<R> where
F: FnOnce(T, U) -> R,` [src]

🔬 This is a nightly-only experimental API. (`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);

Run

### `impl<'_, T> Option<&'_ T> where
T: Copy,` [src]

#### `pub fn copied(self) -> Option<T>`1.35.0[src]

Maps an `Option<&T>` to an `Option<T>` by copying the contents of the option.

# Examples

    let x = 12;
    let opt_x = Some(&x);
    assert_eq!(opt_x, Some(&12));
    let copied = opt_x.copied();
    assert_eq!(copied, Some(12));

Run

### `impl<'_, T> Option<&'_ mut T> where
T: Copy,` [src]

#### `pub fn copied(self) -> Option<T>`1.35.0[src]

Maps an `Option<&mut T>` to an `Option<T>` by copying the contents of the option.

# Examples

    let mut x = 12;
    let opt_x = Some(&mut x);
    assert_eq!(opt_x, Some(&mut 12));
    let copied = opt_x.copied();
    assert_eq!(copied, Some(12));

Run

### `impl<'_, T> Option<&'_ T> where
T: Clone,` [src]

#### `pub fn cloned(self) -> Option<T>`[src]

Maps an `Option<&T>` to an `Option<T>` by cloning the contents of the option.

# Examples

    let x = 12;
    let opt_x = Some(&x);
    assert_eq!(opt_x, Some(&12));
    let cloned = opt_x.cloned();
    assert_eq!(cloned, Some(12));

Run

### `impl<'_, T> Option<&'_ mut T> where
T: Clone,` [src]

#### `pub fn cloned(self) -> Option<T>`1.26.0[src]

Maps an `Option<&mut T>` to an `Option<T>` by cloning the contents of the option.

# Examples

    let mut x = 12;
    let opt_x = Some(&mut x);
    assert_eq!(opt_x, Some(&mut 12));
    let cloned = opt_x.cloned();
    assert_eq!(cloned, Some(12));

Run

### `impl<T> Option<T> where
T: Debug,` [src]

#### `pub fn expect_none(self, msg: &str)`[src]

🔬 This is a nightly-only experimental API. (`option_expect_none` #62633)

newly added

Consumes `self` while expecting `None` and returning nothing.

# Panics

Panics if the value is a `Some`, with a panic message including the passed message, and the content of the `Some`.

# Examples

    #![feature(option_expect_none)]

    use std::collections::HashMap;
    let mut squares = HashMap::new();
    for i in -10..=10 {
        // This will not panic, since all keys are unique.
        squares.insert(i, i * i).expect_none("duplicate key");
    }

Run
ⓘ

    #![feature(option_expect_none)]

    use std::collections::HashMap;
    let mut sqrts = HashMap::new();
    for i in -10..=10 {
        // This will panic, since both negative and positive `i` will
        // insert the same `i * i` key, returning the old `Some(i)`.
        sqrts.insert(i * i, i).expect_none("duplicate key");
    }

Run

#### `pub fn unwrap_none(self)`[src]

🔬 This is a nightly-only experimental API. (`option_unwrap_none` #62633)

newly added

Consumes `self` while expecting `None` and returning nothing.

# Panics

Panics if the value is a `Some`, with a custom panic message provided by the `Some`'s value.

# Examples

    #![feature(option_unwrap_none)]

    use std::collections::HashMap;
    let mut squares = HashMap::new();
    for i in -10..=10 {
        // This will not panic, since all keys are unique.
        squares.insert(i, i * i).unwrap_none();
    }

Run
ⓘ

    #![feature(option_unwrap_none)]

    use std::collections::HashMap;
    let mut sqrts = HashMap::new();
    for i in -10..=10 {
        // This will panic, since both negative and positive `i` will
        // insert the same `i * i` key, returning the old `Some(i)`.
        sqrts.insert(i * i, i).unwrap_none();
    }

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### `impl<T> Option<T> where
T: Default,` [src]

#### `pub fn unwrap_or_default(self) -> T`[src]

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);

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### `impl<T> Option<T> where
T: Deref,` [src]

#### `pub fn as_deref(&self) -> Option<&<T as Deref>::Target>`1.40.0[src]

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);

Run

### `impl<T> Option<T> where
T: DerefMut,` [src]

#### `pub fn as_deref_mut(&mut self) -> Option<&mut <T as Deref>::Target>`1.40.0[src]

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()));

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### `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());

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### `impl<T> Option<Option<T>>`[src]

#### `pub fn flatten(self) -> Option<T>`1.40.0[src]

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());

Run

Flattening 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());

Run

## Trait Implementations

### `impl<T> Clone for Option<T> where
T: Clone,` [src]

#### `pub fn clone(&self) -> Option<T>`[src]

Returns a copy of the value. Read more

#### `pub fn clone_from(&mut self, source: &Option<T>)`[src]

Performs copy-assignment from `source`. Read more

### `impl<T> Copy for Option<T> where
T: Copy,` [src]

### `impl<T> Debug for Option<T> where
T: Debug,` [src]

#### `pub fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>`[src]

Formats the value using the given formatter. Read more

### `impl<T> Default for Option<T>`[src]

#### `pub fn default() -> Option<T>`[src]

Returns `None`.

# Examples

    let opt: Option<u32> = Option::default();
    assert!(opt.is_none());

Run

### `impl<T> Eq for Option<T> where
T: Eq,` [src]

### `impl<'a, T> From<&'a Option<T>> for Option<&'a T>`1.30.0[src]

#### `pub fn from(o: &'a Option<T>) -> Option<&'a 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 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));

Run

### `impl<'a, T> From<&'a mut Option<T>> for Option<&'a mut T>`1.30.0[src]

#### `pub fn from(o: &'a mut Option<T>) -> Option<&'a mut T>`[src]

Converts from `&mut Option<T>` to `Option<&mut T>`

# Examples

    let mut s = Some(String::from("Hello"));
    let o: Option<&mut String> = Option::from(&mut s);

    match o {
        Some(t) => *t = String::from("Hello, Rustaceans!"),
        None => (),
    }

    assert_eq!(s, Some(String::from("Hello, Rustaceans!")));

Run

### `impl<T> From<T> for Option<T>`1.12.0[src]

#### `pub fn from(val: T) -> Option<T>`[src]

Copies `val` into a new `Some`.

# Examples

    let o: Option<u8> = Option::from(67);

    assert_eq!(Some(67), o);

Run

### `impl<A, V> FromIterator<Option<A>> for Option<V> where
V: FromIterator<A>,` [src]

#### `pub fn from_iter<I>(iter: I) -> Option<V> where
I: IntoIterator<Item = Option<A>>,` [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 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]));

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`.

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);

Run

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> Hash for Option<T> where
T: Hash,` [src]

#### `pub fn hash<__H>(&self, state: &mut __H) where
__H: Hasher,` [src]

Feeds this value into the given `Hasher`. Read more

#### `pub fn hash_slice<H>(data: &[Self], state: &mut H) where
H: Hasher,` 1.3.0[src]

Feeds a slice of this type into the given `Hasher`. Read more

### `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?

#### `pub fn into_iter(self) -> IntoIter<T>ⓘ

### Notable traits for IntoIter<A>

`impl<A> Iterator for IntoIter<A> type Item = A;`
`[src]

Returns a consuming iterator over the possibly contained value.

# Examples

    let x = Some("string");
    let v: Vec<&str> = x.into_iter().collect();
    assert_eq!(v, ["string"]);

    let x = None;
    let v: Vec<&str> = x.into_iter().collect();
    assert!(v.is_empty());

Run

### `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?

#### `pub fn into_iter(self) -> IterMut<'a, T>ⓘ

### Notable traits for IterMut<'a, A>

`impl<'a, A> Iterator for IterMut<'a, A> type Item = &'a mut A;`
`[src]

Creates an iterator from a value. Read more

### `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?

#### `pub fn into_iter(self) -> Iter<'a, T>ⓘ

### Notable traits for Iter<'a, A>

`impl<'a, A> Iterator for Iter<'a, A> type Item = &'a A;`
`[src]

Creates an iterator from a value. Read more

### `impl<T> Ord for Option<T> where
T: Ord,` [src]

#### `pub fn cmp(&self, other: &Option<T>) -> Ordering`[src]

This method returns an `Ordering` between `self` and `other`. Read more

#### `#[must_use]pub fn max(self, other: Self) -> Self` 1.21.0[src]

Compares and returns the maximum of two values. Read more

#### `#[must_use]pub fn min(self, other: Self) -> Self` 1.21.0[src]

Compares and returns the minimum of two values. Read more

#### `#[must_use]pub fn clamp(self, min: Self, max: Self) -> Self` 1.50.0[src]

Restrict a value to a certain interval. Read more

### `impl<T> PartialEq<Option<T>> for Option<T> where
T: PartialEq<T>,` [src]

#### `pub fn eq(&self, other: &Option<T>) -> bool`[src]

This method tests for `self` and `other` values to be equal, and is used by `==`. Read more

#### `pub fn ne(&self, other: &Option<T>) -> bool`[src]

This method tests for `!=`.

### `impl<T> PartialOrd<Option<T>> for Option<T> where
T: PartialOrd<T>,` [src]

#### `pub fn partial_cmp(&self, other: &Option<T>) -> Option<Ordering>`[src]

This method returns an ordering between `self` and `other` values if one exists. Read more

#### `pub fn lt(&self, other: &Option<T>) -> bool`[src]

This method tests less than (for `self` and `other`) and is used by the `<` operator. Read more

#### `pub fn le(&self, other: &Option<T>) -> bool`[src]

This method tests less than or equal to (for `self` and `other`) and is used by the `<=` operator. Read more

#### `pub fn gt(&self, other: &Option<T>) -> bool`[src]

This method tests greater than (for `self` and `other`) and is used by the `>` operator. Read more

#### `pub fn ge(&self, other: &Option<T>) -> bool`[src]

This method tests greater than or equal to (for `self` and `other`) and is used by the `>=` operator. Read more

### `impl<T, U> Product<Option<U>> for Option<T> where
T: Product<U>,` 1.37.0[src]

#### `pub fn product<I>(iter: I) -> Option<T> where
I: Iterator<Item = Option<U>>,` [src]

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> StructuralEq for Option<T>`[src]

### `impl<T> StructuralPartialEq for Option<T>`[src]

### `impl<T, U> Sum<Option<U>> for Option<T> where
T: Sum<U>,` 1.37.0[src]

#### `pub fn sum<I>(iter: I) -> Option<T> where
I: Iterator<Item = Option<U>>,` [src]

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));

Run

### `impl<T> Try for Option<T>`[src]

#### `type Ok = T`

🔬 This is a nightly-only experimental API. (`try_trait` #42327)

The type of this value when viewed as successful.

#### `type Error = NoneError`

🔬 This is a nightly-only experimental API. (`try_trait` #42327)

The type of this value when viewed as failed.

#### `pub fn into_result(self) -> Result<T, NoneError>`[src]

🔬 This is a nightly-only experimental API. (`try_trait` #42327)

Applies 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

#### `pub fn from_ok(v: T) -> Option<T>`[src]

🔬 This is a nightly-only experimental API. (`try_trait` #42327)

Wrap an OK value to construct the composite result. For example, `Result::Ok(x)` and `Result::from_ok(x)` are equivalent. Read more

#### `pub fn from_error(NoneError) -> Option<T>`[src]

🔬 This is a nightly-only experimental API. (`try_trait` #42327)

Wrap an error value to construct the composite result. For example, `Result::Err(x)` and `Result::from_error(x)` are equivalent. Read more

## Auto Trait Implementations

### `impl<T> RefUnwindSafe for Option<T> where
T: RefUnwindSafe,` [src]

### `impl<T> Send for Option<T> where
T: Send,` [src]

### `impl<T> Sync for Option<T> where
T: Sync,` [src]

### `impl<T> Unpin for Option<T> where
T: Unpin,` [src]

### `impl<T> UnwindSafe for Option<T> where
T: UnwindSafe,` [src]

## Blanket Implementations

### `impl<T> Any for T where
T: 'static + ?Sized,` [src]

#### `pub fn type_id(&self) -> TypeId`[src]

Gets the `TypeId` of `self`. Read more

### `impl<T> Borrow<T> for T where
T: ?Sized,` [src]

#### `pub fn borrow(&self) -> &Tⓘ

### Notable traits for &'_ mut F

`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 Rimpl<W: Write + ?Sized> Write for &mut W`
`[src]

Immutably borrows from an owned value. Read more

### `impl<T> BorrowMut<T> for T where
T: ?Sized,` [src]

#### `pub fn borrow_mut(&mut self) -> &mut Tⓘ

### Notable traits for &'_ mut F

`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 Rimpl<W: Write + ?Sized> Write for &mut W`
`[src]

Mutably borrows from an owned value. Read more

### `impl<T> From<!> for T`[src]

#### `pub fn from(t: !) -> T`[src]

Performs the conversion.

### `impl<T> From<T> for T`[src]

#### `pub fn from(t: T) -> T`[src]

Performs the conversion.

### `impl<T, U> Into<U> for T where
U: From<T>,` [src]

#### `pub fn into(self) -> U`[src]

Performs the conversion.

### `impl<T> ToOwned for T where
T: Clone,` [src]

#### `type Owned = T`

The resulting type after obtaining ownership.

#### `pub fn to_owned(&self) -> T`[src]

Creates owned data from borrowed data, usually by cloning. Read more

#### `pub fn clone_into(&self, target: &mut T)`[src]

🔬 This is a nightly-only experimental API. (`toowned_clone_into` #41263)

recently added

Uses borrowed data to replace owned data, usually by cloning. Read more

### `impl<T, U> TryFrom<U> for T where
U: Into<T>,` [src]

#### `type Error = Infallible`

The type returned in the event of a conversion error.

#### `pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>`[src]

Performs the conversion.

### `impl<T, U> TryInto<U> for T where
U: TryFrom<T>,` [src]

#### `type Error = <U as TryFrom<T>>::Error`

The type returned in the event of a conversion error.

#### `pub fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>`[src]

Performs the conversion.