core::option::OptionTrait - Starknet Documentation

A trait for handling Option related operations.

Signature

pub trait OptionTrait

Trait functions

expect

Returns the contained Some value, consuming the self value.

Signature

fn expect(self: Option, err: felt252) -> T

Panics

Panics if the option value is None with a custom felt252 panic message err.

Examples

let option = Some(123);
let value = option.expect('no value');
assert!(value == 123);

unwrap

Returns the contained Some value, consuming the self value.

Signature

fn unwrap(self: Option) -> T

Panics

Panics if the self value equals None.

Examples

let option = Some(123);
let value = option.unwrap();
assert!(value == 123);

ok_or

Transforms the Option into a Result, mapping Some(v) to Ok(v) and None to Err(err).

Signature

fn ok_or>(self: Option, err: E) -> Result

Examples

assert_eq!(Some('foo').ok_or(0), Ok('foo'));

let option: Option = None;
assert_eq!(option.ok_or(0), Err(0));

ok_or_else

Transforms the Option into a Result, mapping Some(v) to Ok(v) and None to Err(err()).

Signature

fn ok_or_else, +core::ops::FnOnce[Output: E], +Drop>(
    self: Option, err: F,
) -> Result

Examples

assert_eq!(Some('foo').ok_or_else(|| 0), Ok('foo'));

let option: Option = None;
assert_eq!(option.ok_or_else(|| 0), Err(0));

and

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.

Signature

fn and, +Drop>(self: Option, optb: Option) -> Option

Examples

let x = Some(2);
let y: Option = None;
assert_eq!(x.and(y), None);

let x: Option = None;
let y: Option = Some("foo");
assert_eq!(x.and(y), None);

let x = Some(2);
let y: Option = Some("foo");
assert_eq!(x.and(y), Some("foo"));

let x: Option = None;
let y: Option = None;
assert_eq!(x.and(y), None);

and_then

Returns None if the option is None, otherwise calls f with the wrapped value and returns the result. Some languages call this operation flatmap.

Signature

fn and_then, +core::ops::FnOnce[Output: Option]>(
    self: Option, f: F,
) -> Option

Examples

use core::num::traits::CheckedMul;

let option: Option = checked_mul(2_u32, 2_u32)
    .and_then(|v| Some(format!("{}", v)));
assert_eq!(option, Some("4"));

let option: Option = checked_mul(65536_u32, 65536_u32)
    .and_then(|v| Some(format!("{}", v)));
assert_eq!(option, None); // overflowed!

let option: Option = Option::::None
    .and_then(|v| Some(format!("{}", v)));
assert_eq!(option, None);

or

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.

Signature

fn or>(self: Option, optb: Option) -> Option

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 = None;
let y = None;
assert_eq!(x.or(y), None);

or_else

Returns the option if it contains a value, otherwise calls f and returns the result.

Signature

fn or_else, +core::ops::FnOnce[Output: Option]>(
    self: Option, f: F,
) -> Option

Examples

let nobody = || Option::::None;
let vikings = || Option::::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);

xor

Returns Some if exactly one of self, optb is Some, otherwise returns None.

Signature

fn xor>(self: Option, optb: Option) -> Option

Examples

let x = Some(2);
let y: Option = None;
assert_eq!(x.xor(y), Some(2));

let x: Option = 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 = None;
let y: Option = None;
assert_eq!(x.xor(y), None);

is_some

Returns true if the Option is Some, false otherwise.

Signature

fn is_some(self: @Option) -> bool

Examples

let option = Some(123);
assert!(option.is_some());

is_some_and

Returns true if the Option is Some and the value inside of it matches a predicate.

Signature

fn is_some_and, +core::ops::FnOnce[Output: bool]>(
    self: Option, f: F,
) -> bool

Examples

assert_eq!(Some(2_u8).is_some_and(|x| x > 1), true);
assert_eq!(Some(0_u8).is_some_and(|x| x > 1), false);

let option: Option = None;
assert_eq!(option.is_some_and(|x| x > 1), false);

is_none

Returns true if the Option is None, false otherwise.

Signature

fn is_none(self: @Option) -> bool

Examples

let option = Some(123);
assert!(!option.is_none());

is_none_or

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

Signature

fn is_none_or, +core::ops::FnOnce[Output: bool]>(
    self: Option, f: F,
) -> bool

Examples

assert_eq!(Some(2_u8).is_none_or(|x| x > 1), true);
assert_eq!(Some(0_u8).is_none_or(|x| x > 1), false);

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

unwrap_or

Returns the contained Some value if self is Some(x). Otherwise, returns the provided default.

Signature

fn unwrap_or>(self: Option, default: T) -> T

Examples

let option = Some(123);
assert!(option.unwrap_or(456) == 123);

let option = None;
assert!(option.unwrap_or(456) == 456);

unwrap_or_default

Returns the contained Some value if self is Some(x). Otherwise, returns Default::::default().

Signature

fn unwrap_or_default>(self: Option) -> T

Examples

let option = Some(123);
assert!(option.unwrap_or_default() == 123);

let option: Option = None;
assert!(option.unwrap_or_default() == Default::default());

unwrap_or_else

Returns the contained Some value or computes it from a closure.

Signature

fn unwrap_or_else, impl func: FnOnce, +Drop>(
    self: Option, f: F,
) -> T

Examples

let k = 10;
assert!(Some(4).unwrap_or_else(|| 2 * k) == 4);
assert!(None.unwrap_or_else(|| 2 * k) == 20);

map

Maps an Option to Option by applying a function to a contained value (if Some) or returns None (if None).

Signature

fn map, +core::ops::FnOnce[Output: U]>(
    self: Option, f: F,
) -> Option

Examples

let maybe_some_string: Option = Some("Hello, World!");
// `Option::map` takes self *by value*, consuming `maybe_some_string`
let maybe_some_len = maybe_some_string.map(|s: ByteArray| s.len());
assert!(maybe_some_len == Some(13));

let x: Option = None;
assert!(x.map(|s: ByteArray| s.len()) == None);

map_or

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.

Signature

fn map_or, +Drop, +core::ops::FnOnce[Output: U]>(
    self: Option, default: U, f: F,
) -> U

Examples

assert_eq!(Some("foo").map_or(42, |v: ByteArray| v.len()), 3);

let x: Option = None;
assert_eq!(x.map_or(42, |v: ByteArray| v.len()), 42);

map_or_else

Computes a default function result (if none), or applies a different function to the contained value (if any).

Signature

fn map_or_else,
    +Drop,
    +Drop,
    +core::ops::FnOnce[Output: U],
    +core::ops::FnOnce[Output: U],
>(
    self: Option, default: D, f: F,
) -> U

Examples

let k = 21;

let x = Some("foo");
assert_eq!(x.map_or_else( || 2 * k, |v: ByteArray| v.len()), 3);

let x: Option = None;
assert_eq!(x.map_or_else( || 2 * k, |v: ByteArray| v.len()), 42);

take

Takes the value out of the option, leaving a None in its place.

Signature

fn take(ref self: Option) -> Option

Examples

let mut x = Some(2);
let y = x.take();
assert_eq!(x, None);
assert_eq!(y, Some(2));

let mut x: Option = None;
let y = x.take();
assert_eq!(x, None);
assert_eq!(y, None);

filter

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.

Signature

fn filter[Output: bool], +Destruct, +Destruct>(
    self: Option, predicate: P,
) -> Option

Examples

let is_even = |n: @u32| -> 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));

flatten

Converts from Option> to Option.

Signature

fn flatten(self: Option>) -> Option

Examples

Basic usage:

let x: Option> = Some(Some(6));
assert_eq!(Some(6), x.flatten());

let x: Option> = Some(None);
assert_eq!(None, x.flatten());

let x: Option> = None;
assert_eq!(None, x.flatten());

Flattening only removes one level of nesting at a time:

let x: Option>> = Some(Some(Some(6)));
assert_eq!(Some(Some(6)), x.flatten());
assert_eq!(Some(6), x.flatten().flatten());

Modules

Miscellaneous

​Signature

​Trait functions

​expect

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​unwrap

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​ok_or

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​ok_or_else

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​and

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​and_then

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​or

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​or_else

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​xor

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​is_some

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​is_some_and

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​is_none

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​is_none_or

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​unwrap_or

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​unwrap_or_default

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​unwrap_or_else

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​map

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​map_or

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​map_or_else

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​take

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​filter

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​flatten

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Signature

Trait functions

expect

Signature

Panics

Examples

unwrap

Signature

Panics

Examples

ok_or

Signature

Examples

ok_or_else

Signature

Examples

and

Signature

Examples

and_then

Signature

Examples

or

Signature

Examples

or_else

Signature

Examples

xor

Signature

Examples

is_some

Signature

Examples

is_some_and

Signature

Examples

is_none

Signature

Examples

is_none_or

Signature

Examples

unwrap_or

Signature

Examples

unwrap_or_default

Signature

Examples

unwrap_or_else

Signature

Examples

map

Signature

Examples

map_or

Signature

Examples

map_or_else

Signature

Examples

take

Signature

Examples

filter

Signature

Examples

flatten

Signature

Examples