Enum std::option::Option

pub enum Option<T> {
    /// No value.
    None: (),
    /// Some value of type `T`.
    Some: T,
}
Expand description

A type that represents an optional value, either Some(val) or None.

Variants

None: ()

No value.

Some: T

Some value of type T.

Trait Implementations

pub fn abi_encode(self, buffer: Buffer) -> Buffer

pub fn abi_decode(refmut buffer: BufferReader) -> Self

pub fn eq(self, other: Self) -> bool

pub fn neq(self, other: Self) -> bool

Evaluates if two values of the same type are not equal.

Additional Information

This function is inherited when eq() is implemented.

Arguments

  • other: [Self] - The value of the same type.

Returns

  • [bool] - true if the two values are not equal, otherwise false.

Examples

struct MyStruct {
    val: u64,
}

impl Eq for MyStruct {
    fn eq(self, other: Self) -> bool {
         self.val == other.val
    }
}

fn foo() {
    let struct1 = MyStruct { val: 10 };
    let struct2 = MyStruct { val: 2 };
    let result = struct1 != struct2;
    assert(result);
}

pub fn is_some(self) -> bool

Returns whether the option is the Some variant.

Returns

  • [bool] - Returns true if the option is Some, otherwise false.

Examples

fn foo() {
    let x: Option<u32> = Some(2);
    assert(x.is_some());

    let x: Option<u32> = None;
    assert(!x.is_some());
}

pub fn is_none(self) -> bool

Returns whether the option is the None variant.

Returns

  • [bool] - Returns true if the option is None, otherwise false.

Examples

fn foo() {
    let x: Option<u32> = Some(2);
    assert(!x.is_none());

    let x: Option<u32> = None;
    assert(x.is_none());
}

pub fn unwrap(self) -> T

Returns the contained Some value, consuming the self value.

Additional Information

Because this function may revert, its use is generally discouraged.
Instead, use pattern matching and handle the None
case explicitly, or call unwrap_or.

Returns

  • [T] - The value contained by the option.

Reverts

  • Reverts if the Option is the None variant.

Examples

fn foo() {
    let x = Some(42);
    assert(x.unwrap() == 42);
}

fn foo() {
    let x: Option<u64> = None;
    let value = x.unwrap(); // reverts
}

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

Returns the contained Some value or a provided default.

Arguments

  • default: [T] - The default value the function will revert to.

Returns

  • [T] - The contained value or the default value.

Examples

fn foo() {
    assert(Some(42).unwrap_or(69) == 42);
    assert(None::<u64>().unwrap_or(69) == 69);
}

pub fn ok_or(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(e).

Additional Information

Ok(v) : Result::Ok
Err(e) : Result::Err
Some(v): Option::Some
ok_or : Option::ok_or

Arguments

  • err: [E] - The error value if the option is None.

Returns

  • [Result<T, E>] - The result containing the value or the error.

Examples

fn foo() {
    let x = Some(42);
    match x.ok_or(0) {
        Result::Ok(inner) => assert(inner == 42),
        Result::Err => revert(0),
    }

    let x: Option<u64> = None;
    match x.ok_or(0) {
        Result::Ok(_) => revert(0),
        Result::Err(e) => assert(e == 0),
    }
}

pub fn expect(self, msg: M) -> T

Returns the contained Some value, consuming the self value.
If the Option is the None variant, logs the provided message.

Additional Information

Because this function may revert, its use is generally discouraged.
Instead, prefer to use pattern matching and handle the None
case explicitly.

Arguments

  • msg: [M] - The message to be logged if the Option is the None variant.

Returns

  • [T] - The value contained by the option.

Reverts

  • Reverts if the Option is the None variant.

Examples


fn foo() {
    let x: Option<u64> = Some(42);
    assert(x.expect("X is known to be 42") == 42);

    let y: Option<u64> = None;
    let val = y.expect("Testing expect"); // reverts with `("Testing Expect")`
}

Recommended Message Style

We recommend that expect messages are used to describe the reason you expect the Option should be Some.

let x: Option<u64> = bar(1);
let value = x.expect("bar() should never return None with 1 as an argument");