Mojo struct

Optional

struct Optional[T: Copyable & Movable]

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 Copyable & Movable so we can implement copy/move for Optional and allow it to be used in collections itself.

Examples:

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

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 (Copyable & Movable): The type of value stored in the Optional.

Implemented traits

AnyType, Boolable, Copyable, ExplicitlyCopyable, Movable, UnknownDestructibility

Methods

__init__

__init__(out self)

Construct an empty Optional.

@implicit __init__(out self, owned value: T)

Construct an Optional containing a value.

Args:

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

@implicit __init__(out self, value: NoneType)

Construct an empty Optional.

Args:

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

__bool__

__bool__(self) -> Bool

Return true if the Optional has a value.

Returns:

True if the Optional has a value and False otherwise.

__getitem__

__getitem__(ref self) -> ref [$1._value] T

Retrieve a reference to the value inside the Optional.

Returns:

A reference to the value inside the Optional.

Raises:

On empty Optional.

__invert__

__invert__(self) -> Bool

Return False if the Optional has a value.

Returns:

False if the Optional has a value and True otherwise.

__eq__

__eq__(self, rhs: NoneType) -> Bool

Return True if a value is not present.

Args:

• ​rhs (NoneType): The None value to compare to.

Returns:

True if a value is not present, False otherwise.

__eq__[T: EqualityComparable & Copyable & Movable](self: Optional[T], rhs: Optional[T]) -> Bool

Return True if this is the same as another Optional value, meaning both are absent, or both are present and have the same underlying value.

Parameters:

• ​T (EqualityComparable & Copyable & Movable): The type of the elements in the list. Must implement the traits Copyable, Movable and EqualityComparable.

Args:

• ​rhs (Optional[T]): The value to compare to.

Returns:

True if the values are the same.

__ne__

__ne__(self, rhs: NoneType) -> Bool

Return True if a value is present.

Args:

• ​rhs (NoneType): The None value to compare to.

Returns:

False if a value is not present, True otherwise.

__ne__[T: EqualityComparable & Copyable & Movable, //](self: Optional[T], rhs: Optional[T]) -> Bool

Return False if this is the same as another Optional value, meaning both are absent, or both are present and have the same underlying value.

Parameters:

• ​T (EqualityComparable & Copyable & Movable): The type of the elements in the list. Must implement the traits Copyable, Movable and EqualityComparable.

Args:

• ​rhs (Optional[T]): The value to compare to.

Returns:

False if the values are the same.

__is__

__is__(self, other: NoneType) -> Bool

Return True if the Optional has no value.

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

Args:

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

Returns:

True if the Optional has no value and False otherwise.

__isnot__

__isnot__(self, other: NoneType) -> Bool

Return True if the Optional has a value.

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

Args:

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

Returns:

True if the Optional has a value and False otherwise.

copy

copy(self) -> Self

Copy construct an Optional.

Returns:

A copy of the value.

__str__

__str__[U: Copyable & Movable & Representable, //](self: Optional[U]) -> String

Return the string representation of the value of the Optional.

Parameters:

• ​U (Copyable & Movable & Representable): The type of the elements in the list. Must implement the traits Representable, Copyable and Movable.

Returns:

A string representation of the Optional.

__repr__

__repr__[U: Representable & Copyable & Movable, //](self: Optional[U]) -> String

Returns the verbose string representation of the Optional.

Parameters:

• ​U (Representable & Copyable & Movable): The type of the elements in the list. Must implement the traits Representable, Copyable and Movable.

Returns:

A verbose string representation of the Optional.

write_to

write_to[W: Writer, U: Representable & Copyable & Movable, //](self: Optional[U], mut writer: W)

Write Optional string representation to a Writer.

Parameters:

• ​W (Writer): A type conforming to the Writable trait.
• ​U (Representable & Copyable & Movable): The type of the elements in the list. Must implement the traits Representable, Copyable and Movable.

Args:

• ​writer (W): The object to write to.

value

value(ref self) -> ref [$1._value] T

Retrieve a reference to the value of the Optional.

Notes: This will abort on empty Optional.

Returns:

A reference to the contained data of the Optional as a reference.

unsafe_value

unsafe_value(ref self) -> ref [$1._value] T

Unsafely retrieve a reference to the value of the Optional.

Notes: This will not abort on empty Optional.

Returns:

A reference to the contained data of the Optional as a reference.

take

take(mut self) -> T

Move the value out of the Optional.

Notes: This will abort on empty Optional.

Returns:

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

unsafe_take

unsafe_take(mut self) -> T

Unsafely move the value out of the Optional.

Notes: This will not abort on empty Optional.

Returns:

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

or_else

or_else(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.

copied

copied[mut: Bool, origin: Origin[mut], //, T: Copyable & Movable](self: Optional[Pointer[T, origin]]) -> Optional[T]

Converts an Optional containing a Pointer to an Optional of an owned value by copying.

Examples:

Copy the value of an Optional[Pointer[_]]

var data = String("foo")
var opt = Optional(Pointer(to=data))
var opt_owned: Optional[String] = opt.copied()

var data = String("foo")
var opt = Optional(Pointer(to=data))
var opt_owned: Optional[String] = opt.copied()

Notes: If self is an empty Optional, the returned Optional will be empty as well.

Parameters:

• ​mut (Bool): Mutability of the pointee origin.
• ​origin (Origin[mut]): Origin of the contained Pointer.
• ​T (Copyable & Movable): Type of the owned result value.

Returns:

An Optional containing an owned copy of the pointee value.

Was this page helpful?

Thank you! We'll create more content like this.

Thank you for helping us improve!

😔 What went wrong?

Some code doesn’t work

It includes inaccurate information

It's missing information I need

It was difficult to understand

Other

Submit