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Option<T> Type

The Option<T> type is a way to express that a value might be present (Some(T)) or absent (None). It's a safer way to handle potential absence of values, compared to using nulls in many other languages.

struct Option<T> {
    None,
    Some(T),
}

The Option type, already imported into your Noir program, can be used directly:

fn main() {
    let none = Option::none();
    let some = Option::some(3);
}

See this test for a more comprehensive set of examples of each of the methods described below.

Methods​

none​

Constructs a none value.

some​

Constructs a some wrapper around a given value.

is_none​

Returns true if the Option is None.

is_some​

Returns true of the Option is Some.

unwrap​

Asserts self.is_some() and returns the wrapped value.

unwrap_unchecked​

Returns the inner value without asserting self.is_some(). This method can be useful within an if condition when we already know that option.is_some(). If the option is None, there is no guarantee what value will be returned, only that it will be of type T for an Option<T>.

unwrap_or​

Returns the wrapped value if self.is_some(). Otherwise, returns the given default value.

unwrap_or_else​

Returns the wrapped value if self.is_some(). Otherwise, calls the given function to return a default value.

expect​

Asserts self.is_some() with a provided custom message and returns the contained Some value. The custom message is expected to be a format string.

map​

If self is Some(x), this returns Some(f(x)). Otherwise, this returns None.

map_or​

If self is Some(x), this returns f(x). Otherwise, this returns the given default value.

map_or_else​

If self is Some(x), this returns f(x). Otherwise, this returns default().

and​

Returns None if self is None. Otherwise, this returns other.

and_then​

If self is None, this returns None. Otherwise, this calls the given function with the Some value contained within self, and returns the result of that call. In some languages this function is called flat_map or bind.

or​

If self is Some, return self. Otherwise, return other.

or_else​

If self is Some, return self. Otherwise, return default().

xor​

If only one of the two Options is Some, return that option. Otherwise, if both options are Some or both are None, None is returned.

filter​

Returns Some(x) if self is Some(x) and predicate(x) is true. Otherwise, this returns None.

flatten​

Flattens an Option<Option<T>> into a Option<T>. This returns None if the outer Option is None. Otherwise, this returns the inner Option.