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§

source§

impl<T> Option<T>

const: 1.48.0 · source

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);
1.70.0 · source

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);
const: 1.48.0 · source

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);
const: 1.48.0 · source

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:?}");
const: unstable · source

pub 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));
1.33.0 (const: unstable) · source

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

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

1.33.0 (const: unstable) · source

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

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

1.75.0 · source

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][..], &[][..]],
);

The inverse of this function is (discounting borrowing) [_]::first:

for i in [Some(1234_u16), None] {
    assert_eq!(i.as_ref(), i.as_slice().first());
}
1.75.0 · source

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 [][..]],
);

The 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));

The inverse of this method (discounting borrowing) is [_]::first_mut:

assert_eq!(Some(123).as_mut_slice().first_mut(), Some(&mut 123))
const: unstable · source

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

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");

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 · source

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

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");
source

pub fn unwrap_or_else<F>(self, f: F) -> T
where F: FnOnce() -> T,

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);
source

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
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);
1.58.0 (const: unstable) · source

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");
let x: Option<&str> = None;
assert_eq!(unsafe { x.unwrap_unchecked() }, "air"); // Undefined behavior!
source

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);
1.76.0 · source

pub fn inspect<F>(self, f: F) -> Option<T>
where F: FnOnce(&T),

Calls the provided closure with a reference to the contained value (if Some).

§Examples
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}"));
source

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);
source

pub fn map_or_else<U, D, F>(self, default: D, f: F) -> U
where D: FnOnce() -> U, F: FnOnce(T) -> 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);
§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()?;
source

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));
source

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));
1.40.0 · source

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);
1.40.0 · source

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()));
const: unstable · source

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

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);
source

pub fn iter_mut(&mut self) -> IterMut<'_, T>

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);
source

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);
source

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);

Often 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);
1.27.0 · source

pub fn filter<P>(self, predicate: P) -> Option<T>
where P: FnOnce(&T) -> bool,

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));
source

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);
source

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);
1.37.0 · source

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);
1.53.0 · source

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);
1.20.0 · source

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));
source

pub fn get_or_insert_default(&mut self) -> &mut T
where T: Default,

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

Inserts the default value into the option if it is None, then returns a mutable reference to the contained value.

§Examples
#![feature(option_get_or_insert_default)]

let mut x = None;

{
    let y: &mut u32 = x.get_or_insert_default();
    assert_eq!(y, &0);

    *y = 7;
}

assert_eq!(x, Some(7));
1.20.0 · source

pub fn get_or_insert_with<F>(&mut self, f: F) -> &mut T
where F: FnOnce() -> T,

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));
const: unstable · source

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

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);
source

pub fn take_if<P>(&mut self, predicate: P) -> Option<T>
where P: FnOnce(&mut T) -> bool,

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

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));
1.31.0 (const: unstable) · source

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);
1.46.0 · source

pub fn zip<U>(self, other: Option<U>) -> Option<(T, U)>

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);
source

pub 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)

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);
source§

impl<T, U> Option<(T, U)>

1.66.0 · source

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));
source§

impl<T> Option<&T>

1.35.0 (const: unstable) · source

pub fn copied(self) -> Option<T>
where T: Copy,

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));
source

pub fn cloned(self) -> Option<T>
where T: Clone,

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));
source§

impl<T> Option<&mut T>

1.35.0 (const: unstable) · source

pub fn copied(self) -> Option<T>
where T: Copy,

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));
1.26.0 · source

pub fn cloned(self) -> Option<T>
where T: Clone,

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));
source§

impl<T, E> Option<Result<T, E>>

1.33.0 (const: unstable) · source

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());
source§

impl<T> Option<Option<T>>

1.40.0 (const: unstable) · source

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());

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());

Trait Implementations§

source§

impl<X, T> Categorize<X> for Option<T>
where X: CustomValueKind,

source§

impl<T> Clone for Option<T>
where T: Clone,

source§

fn clone(&self) -> Option<T>

Returns a copy of the value. Read more
source§

fn clone_from(&mut self, source: &Option<T>)

Performs copy-assignment from source. Read more
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impl<T> Context<T, Infallible> for Option<T>

use anyhow::{Context, Result};

fn maybe_get() -> Option<T> {
    ...
}

fn demo() -> Result<()> {
    let t = maybe_get().context("there is no T")?;
    ...
}
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fn context<C>(self, context: C) -> Result<T, Error>
where C: Display + Send + Sync + 'static,

Wrap the error value with additional context.
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fn with_context<C, F>(self, context: F) -> Result<T, Error>
where C: Display + Send + Sync + 'static, F: FnOnce() -> C,

Wrap the error value with additional context that is evaluated lazily only once an error does occur.
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impl<T> Debug for Option<T>
where T: Debug,

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fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter. Read more
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impl<X, D, T> Decode<X, D> for Option<T>
where X: CustomValueKind, D: Decoder<X>, T: Decode<X, D>,

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fn decode_body_with_value_kind( decoder: &mut D, value_kind: ValueKind<X> ) -> Result<Option<T>, DecodeError>

Decodes the type from the decoder, which should match a preloaded value kind. Read more
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impl<T> Default for Option<T>

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fn default() -> Option<T>

Returns None.

§Examples
let opt: Option<u32> = Option::default();
assert!(opt.is_none());
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impl<C, T> Describe<C> for Option<T>

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const TYPE_ID: RustTypeId = _

The TYPE_ID should give a unique identifier for its SBOR schema type. An SBOR schema type capture details about the SBOR payload, how it should be interpreted, validated and displayed. Read more
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fn type_data() -> TypeData<C, RustTypeId>

Returns the local schema for the given type. Read more
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fn add_all_dependencies(aggregator: &mut TypeAggregator<C>)

For each type referenced in get_local_type_data, we need to ensure that the type and all of its own references get added to the aggregator. Read more
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impl<'de, T> Deserialize<'de> for Option<T>
where T: Deserialize<'de>,

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fn deserialize<D>( deserializer: D ) -> Result<Option<T>, <D as Deserializer<'de>>::Error>
where D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer. Read more
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impl<X, E, T> Encode<X, E> for Option<T>
where X: CustomValueKind, E: Encoder<X>, T: Encode<X, E>,

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fn encode_value_kind(&self, encoder: &mut E) -> Result<(), EncodeError>

Encodes the SBOR value’s kind to the encoder
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fn encode_body(&self, encoder: &mut E) -> Result<(), EncodeError>

Encodes the SBOR body of the type to the encoder. Read more
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impl<T> Encode for Option<T>
where T: Encode,

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fn encode(&self, sink: &mut Vec<u8>)

Encode the type into the given byte sink.
1.30.0 · source§

impl<'a, T> From<&'a Option<T>> for Option<&'a T>

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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));
1.30.0 · source§

impl<'a, T> From<&'a mut Option<T>> for Option<&'a mut T>

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fn from(o: &'a mut Option<T>) -> Option<&'a mut T>

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!")));
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impl<T> From<CtOption<T>> for Option<T>

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fn from(source: CtOption<T>) -> Option<T>

Convert the CtOption<T> wrapper into an Option<T>, depending on whether the underlying is_some Choice was a 0 or a 1 once unwrapped.

§Note

This function exists to avoid ending up with ugly, verbose and/or bad handled conversions from the CtOption<T> wraps to an Option<T> or Result<T, E>. This implementation doesn’t intend to be constant-time nor try to protect the leakage of the T since the Option<T> will do it anyways.

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impl<'a> From<Option<&'a AddressBech32Encoder>> for AddressDisplayContext<'a>

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fn from(encoder: Option<&'a AddressBech32Encoder>) -> AddressDisplayContext<'a>

Converts to this type from the input type.
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impl<'a> From<Option<&'a AddressBech32Encoder>> for TransactionReceiptDisplayContext<'a>

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fn from(encoder: Option<&'a AddressBech32Encoder>) -> Self

Converts to this type from the input type.
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impl<'a> From<Option<&'a TransactionHashBech32Encoder>> for TransactionHashDisplayContext<'a>

§

fn from( encoder: Option<&'a TransactionHashBech32Encoder> ) -> TransactionHashDisplayContext<'a>

Converts to this type from the input type.
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impl From<Option<AttachedModuleId>> for ModuleId

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fn from(value: Option<AttachedModuleId>) -> ModuleId

Converts to this type from the input type.
1.12.0 · source§

impl<T> From<T> for Option<T>

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fn from(val: T) -> Option<T>

Moves val into a new Some.

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

assert_eq!(Some(67), o);
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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>>,

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]));

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.

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impl<'a> FromReader<'a> for Option<ComponentValType>

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fn from_reader( reader: &mut BinaryReader<'a> ) -> Result<Option<ComponentValType>, BinaryReaderError>

Attempts to read Self from the provided binary reader, returning an error if it is unable to do so.
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impl<T> FromResidual<Yeet<()>> for Option<T>

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fn from_residual(_: Yeet<()>) -> Option<T>

🔬This is a nightly-only experimental API. (try_trait_v2)
Constructs the type from a compatible Residual type. Read more
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impl<T> FromResidual for Option<T>

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fn from_residual(residual: Option<Infallible>) -> Option<T>

🔬This is a nightly-only experimental API. (try_trait_v2)
Constructs the type from a compatible Residual type. Read more
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impl<T> Hash for Option<T>
where T: Hash,

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fn hash<__H>(&self, state: &mut __H)
where __H: Hasher,

Feeds this value into the given Hasher. Read more
1.3.0 · source§

fn hash_slice<H>(data: &[Self], state: &mut H)
where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher. Read more
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impl<'a> Into<ManifestDecompilationDisplayContext<'a>> for Option<&'a AddressBech32Encoder>

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fn into(self) -> ManifestDecompilationDisplayContext<'a>

Converts this type into the (usually inferred) input type.
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impl<'a> Into<ManifestValueDisplayContext<'a>> for Option<&'a AddressBech32Encoder>

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fn into(self) -> ManifestValueDisplayContext<'a>

Converts this type into the (usually inferred) input type.
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impl Into<Option<AttachedModuleId>> for ModuleId

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fn into(self) -> Option<AttachedModuleId>

Converts this type into the (usually inferred) input type.
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impl<'a> Into<ScryptoValueDisplayContext<'a>> for Option<&'a AddressBech32Encoder>

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fn into(self) -> ScryptoValueDisplayContext<'a>

Converts this type into the (usually inferred) input type.
1.4.0 · source§

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?
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fn into_iter(self) -> Iter<'a, T>

Creates an iterator from a value. Read more
1.4.0 · source§

impl<'a, T> IntoIterator for &'a mut Option<T>

§

type Item = &'a mut T

The type of the elements being iterated over.
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type IntoIter = IterMut<'a, T>

Which kind of iterator are we turning this into?
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fn into_iter(self) -> IterMut<'a, T>

Creates an iterator from a value. Read more
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impl<T> IntoIterator for Option<T>

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fn into_iter(self) -> IntoIter<T>

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());
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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?
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impl<T> Ord for Option<T>
where T: Ord,

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fn cmp(&self, other: &Option<T>) -> Ordering

This method returns an Ordering between self and other. Read more
1.21.0 · source§

fn max(self, other: Self) -> Self
where Self: Sized,

Compares and returns the maximum of two values. Read more
1.21.0 · source§

fn min(self, other: Self) -> Self
where Self: Sized,

Compares and returns the minimum of two values. Read more
1.50.0 · source§

fn clamp(self, min: Self, max: Self) -> Self
where Self: Sized + PartialOrd,

Restrict a value to a certain interval. Read more
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impl Parse for Option<Abi>

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impl Parse for Option<BoundLifetimes>

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impl Parse for Option<Label>

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impl<T> Parse for Option<T>
where T: Parse + Token,

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fn parse(input: &ParseBuffer<'_>) -> Result<Option<T>, Error>

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impl Parse for Option<WhereClause>

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impl<T> PartialEq for Option<T>
where T: PartialEq,

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fn eq(&self, other: &Option<T>) -> bool

This method tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl<T> PartialOrd for Option<T>
where T: PartialOrd,

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fn partial_cmp(&self, other: &Option<T>) -> Option<Ordering>

This method returns an ordering between self and other values if one exists. Read more
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fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator. Read more
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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
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fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator. Read more
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fn ge(&self, other: &Rhs) -> bool

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

impl<T, U> Product<Option<U>> for Option<T>
where T: Product<U>,

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fn product<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 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);
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impl<T> Residual<T> for Option<Infallible>

§

type TryType = Option<T>

🔬This is a nightly-only experimental API. (try_trait_v2_residual)
The “return” type of this meta-function.
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impl<T> Serialize for Option<T>
where T: Serialize,

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fn serialize<S>( &self, serializer: S ) -> Result<<S as Serializer>::Ok, <S as Serializer>::Error>
where S: Serializer,

Serialize this value into the given Serde serializer. Read more
1.37.0 · source§

impl<T, U> Sum<Option<U>> for Option<T>
where T: Sum<U>,

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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));
let words = vec!["have", "a", "good", "day"];
let total: Option<usize> = words.iter().map(|w| w.find('a')).sum();
assert_eq!(total, None);
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impl ToMetadataEntry for Option<GenericMetadataValue<UncheckedUrl, UncheckedOrigin>>

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impl ToRoleEntry for Option<AccessRule>

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impl<T> ToTokens for Option<T>
where T: ToTokens,

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fn to_tokens(&self, tokens: &mut TokenStream)

Write self to the given TokenStream. Read more
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fn to_token_stream(&self) -> TokenStream

Convert self directly into a TokenStream object. Read more
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fn into_token_stream(self) -> TokenStream
where Self: Sized,

Convert self directly into a TokenStream object. Read more
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impl<T> Try for Option<T>

§

type Output = T

🔬This is a nightly-only experimental API. (try_trait_v2)
The type of the value produced by ? when not short-circuiting.
§

type Residual = Option<Infallible>

🔬This is a nightly-only experimental API. (try_trait_v2)
The type of the value passed to FromResidual::from_residual as part of ? when short-circuiting. Read more
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fn from_output(output: <Option<T> as Try>::Output) -> Option<T>

🔬This is a nightly-only experimental API. (try_trait_v2)
Constructs the type from its Output type. Read more
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fn branch( self ) -> ControlFlow<<Option<T> as Try>::Residual, <Option<T> as Try>::Output>

🔬This is a nightly-only experimental API. (try_trait_v2)
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
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impl<Z> Zeroize for Option<Z>
where Z: Zeroize,

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fn zeroize(&mut self)

Zero out this object from memory using Rust intrinsics which ensure the zeroization operation is not “optimized away” by the compiler.
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impl<T> Copy for Option<T>
where T: Copy,

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impl<T> Eq for Option<T>
where T: Eq,

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impl<T> StructuralPartialEq for Option<T>

Auto Trait Implementations§

§

impl<T> RefUnwindSafe for Option<T>
where T: RefUnwindSafe,

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impl<T> Send for Option<T>
where T: Send,

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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§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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impl<U> As for U

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fn as_<T>(self) -> T
where T: CastFrom<U>,

Casts self to type T. The semantics of numeric casting with the as operator are followed, so <T as As>::as_::<U> can be used in the same way as T as U for numeric conversions. Read more
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impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> CallHasher for T
where T: Hash + ?Sized,

§

fn get_hash<H, B>(value: &H, build_hasher: &B) -> u64
where H: Hash + ?Sized, B: BuildHasher,

§

impl<T1> DecodeUntypedSlice for T1
where T1: From<UntypedValue>,

§

fn decode_untyped_slice(results: &[UntypedValue]) -> Result<T1, UntypedError>

Decodes the slice of [UntypedValue] as a value of type Self. Read more
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impl<T> Downcast for T
where T: Any,

§

fn into_any(self: Box<T>) -> Box<dyn Any>

Convert Box<dyn Trait> (where Trait: Downcast) to Box<dyn Any>. Box<dyn Any> can then be further downcast into Box<ConcreteType> where ConcreteType implements Trait.
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fn into_any_rc(self: Rc<T>) -> Rc<dyn Any>

Convert Rc<Trait> (where Trait: Downcast) to Rc<Any>. Rc<Any> can then be further downcast into Rc<ConcreteType> where ConcreteType implements Trait.
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fn as_any(&self) -> &(dyn Any + 'static)

Convert &Trait (where Trait: Downcast) to &Any. This is needed since Rust cannot generate &Any’s vtable from &Trait’s.
§

fn as_any_mut(&mut self) -> &mut (dyn Any + 'static)

Convert &mut Trait (where Trait: Downcast) to &Any. This is needed since Rust cannot generate &mut Any’s vtable from &mut Trait’s.
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impl<T> DowncastSync for T
where T: Any + Send + Sync,

§

fn into_any_arc(self: Arc<T>) -> Arc<dyn Any + Send + Sync>

Convert Arc<Trait> (where Trait: Downcast) to Arc<Any>. Arc<Any> can then be further downcast into Arc<ConcreteType> where ConcreteType implements Trait.
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impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

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fn equivalent(&self, key: &K) -> bool

Compare self to key and return true if they are equal.
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impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

§

fn equivalent(&self, key: &K) -> bool

Checks if this value is equivalent to the given key. Read more
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impl<Q, K> Equivalent<K> for Q
where Q: Eq + ?Sized, K: Borrow<Q> + ?Sized,

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fn equivalent(&self, key: &K) -> bool

Compare self to key and return true if they are equal.
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impl<T> From<!> for T

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fn from(t: !) -> T

Converts to this type from the input type.
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

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impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

§

impl<T> Pointable for T

§

const ALIGN: usize = _

The alignment of pointer.
§

type Init = T

The type for initializers.
§

unsafe fn init(init: <T as Pointable>::Init) -> usize

Initializes a with the given initializer. Read more
§

unsafe fn deref<'a>(ptr: usize) -> &'a T

Dereferences the given pointer. Read more
§

unsafe fn deref_mut<'a>(ptr: usize) -> &'a mut T

Mutably dereferences the given pointer. Read more
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unsafe fn drop(ptr: usize)

Drops the object pointed to by the given pointer. Read more
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impl<T> Same for T

§

type Output = T

Should always be Self
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impl<T> Spanned for T
where T: Spanned + ?Sized,

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fn span(&self) -> Span

Returns a Span covering the complete contents of this syntax tree node, or Span::call_site() if this node is empty.
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impl<T> ToOwned for T
where T: Clone,

§

type Owned = T

The resulting type after obtaining ownership.
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fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more
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impl<T, U> TryFrom<U> for T
where U: Into<T>,

§

type Error = Infallible

The type returned in the event of a conversion error.
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

§

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

The type returned in the event of a conversion error.
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fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.
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impl<V, T> VZip<V> for T
where V: MultiLane<T>,

§

fn vzip(self) -> V

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impl<T> BasicCategorize for T

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impl<T> BasicDecode for T

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impl<T> BasicDescribe for T

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impl<T> BasicEncode for T

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impl<T> BasicSbor for T

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impl<T> DeserializeOwned for T
where T: for<'de> Deserialize<'de>,

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impl<T> ManifestCategorize for T

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impl<T> ManifestDecode for T

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impl<T> ManifestEncode for T

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impl<T> ScryptoCategorize for T

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impl<T> ScryptoDecode for T

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impl<T> ScryptoDescribe for T

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impl<T> ScryptoEncode for T

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impl<T> ScryptoSbor for T