Enum 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 of type T.

Implementations

impl<T> Option<T>

pub const fn is_some(&self) -> bool

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);

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);

let x: Option<String> = Some("ownership".to_string());
assert_eq!(x.as_ref().is_some_and(|x| x.len() > 1), true);
println!("still alive {:?}", x);

pub const fn is_none(&self) -> bool

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);

pub fn is_none_or(self, f: impl FnOnce(T) -> bool) -> bool

Returns true if the option is a None or the value inside of it matches a predicate.

Examples

let x: Option<u32> = Some(2);
assert_eq!(x.is_none_or(|x| x > 1), true);

let x: Option<u32> = Some(0);
assert_eq!(x.is_none_or(|x| x > 1), false);

let x: Option<u32> = None;
assert_eq!(x.is_none_or(|x| x > 1), true);

let x: Option<String> = Some("ownership".to_string());
assert_eq!(x.as_ref().is_none_or(|x| x.len() > 1), true);
println!("still alive {:?}", x);

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:?}");

pub const fn as_mut(&mut self) -> Option<&mut T>

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));

pub const fn as_pin_ref(self: Pin<&Option<T>>) -> Option<Pin<&T>>

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

pub const fn as_pin_mut(self: Pin<&mut Option<T>>) -> Option<Pin<&mut T>>

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

pub const 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(),