struct

Optional

A type modeling a value which may or may not be present.

Optional values can be thought of as a type-safe nullable pattern. Your value can take on a value or None, and you need to check and explicitly extract the value to get it out.

Currently T is required to be a CollectionElement so we can implement copy/move for Optional and allow it to be used in collections itself.

from collections import Optional
var a = Optional(1)
var b = Optional[Int](None)
if a:
    print(a.value()[])  # prints 1
if b:  # bool(b) is False, so no print
    print(b.value()[])
var c = a.or_else(2)
var d = b.or_else(2)
print(c)  # prints 1
print(d)  # prints 2

Parameters

• ​T (CollectionElement): The type of value stored in the Optional.

Implemented traits

AnyType, Boolable, CollectionElement, Copyable, Movable

Methods

__init__

__init__(inout self: Self)

Construct an empty Optional.

__init__(inout self: Self, owned value: T)

Construct an Optional containing a value.

Args:

• ​value (T): The value to store in the optional.

__init__(inout self: Self, value: None)

Construct an empty Optional.

Args:

• ​value (None): Must be exactly None.

__bool__

__bool__(self: Self) -> Bool

Return true if the Optional has a value.

Returns:

True if the optional has a value and False otherwise.

__invert__

__invert__(self: Self) -> Bool

Return False if the optional has a value.

Returns:

False if the optional has a value and True otherwise.

__is__

__is__(self: Self, other: None) -> Bool

Return True if the Optional has no value.

It allows you to use the following syntax: if my_optional is None:

Args:

• ​other (None): The value to compare to (None).

Returns:

True if the Optional has no value and False otherwise.

__isnot__

__isnot__(self: Self, other: None) -> Bool

Return True if the Optional has a value.

It allows you to use the following syntax: if my_optional is not None:.

Args:

• ​other (None): The value to compare to (None).

Returns:

True if the Optional has a value and False otherwise.

value

value(self: Reference[Optional[T], is_mutable, lifetime, 0]) -> Reference[T, $0, $1, 0]

Retrieve a reference to the value of the Optional.

This check to see if the optional contains a value. If you call this without first verifying the optional with bool() eg. by if my_option: or without otherwise knowing that it contains a value (for instance with or_else), the program will abort

Returns:

A reference to the contained data of the option as a Reference[T].

unsafe_value

unsafe_value(self: Reference[Optional[T], is_mutable, lifetime, 0]) -> Reference[T, $0, $1, 0]

Unsafely retrieve a reference to the value of the Optional.

This doesn't check to see if the optional contains a value. If you call this without first verifying the optional with bool() eg. by if my_option: or without otherwise knowing that it contains a value (for instance with or_else), you'll get garbage unsafe data out.

Returns:

A reference to the contained data of the option as a Reference[T].

take

take(inout self: Self) -> T

Move the value out of the Optional.

The caller takes ownership over the new value, which is moved out of the Optional, and the Optional is left in an empty state.

This check to see if the optional contains a value. If you call this without first verifying the optional with bool() eg. by if my_option: or without otherwise knowing that it contains a value (for instance with or_else), you'll get garbage unsafe data out.

Returns:

The contained data of the option as an owned T value.

unsafe_take

unsafe_take(inout self: Self) -> T

Unsafely move the value out of the Optional.

The caller takes ownership over the new value, which is moved out of the Optional, and the Optional is left in an empty state.

This check to see if the optional contains a value. If you call this without first verifying the optional with bool() eg. by if my_option: or without otherwise knowing that it contains a value (for instance with or_else), the program will abort!

Returns:

The contained data of the option as an owned T value.

or_else

or_else(self: Self, default: T) -> T

Return the underlying value contained in the Optional or a default value if the Optional's underlying value is not present.

Args:

• ​default (T): The new value to use if no value was present.

Returns:

The underlying value contained in the Optional or a default value.