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Version: v0.29.0

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.