Mojo struct

Variant

struct Variant[*Ts: Copyable & Movable]

A runtime-variant type.

Data for this type is stored internally. Currently, its size is the largest size of any of its variants plus a 16-bit discriminant.

You can - use isa[T]() to check what type a variant is - use unsafe_take[T]() to take a value from the variant - use [T] to get a value out of a variant - This currently does an extra copy/move until we have origins - It also temporarily requires the value to be mutable - use set[T](var new_value: T) to reset the variant to a new value - use is_type_supported[T] to check if the variant permits the type T

Example:

from utils import Variant
alias IntOrString = Variant[Int, String]
fn to_string(mut x: IntOrString) -> String:
    if x.isa[String]():
        return x[String]
    # x.isa[Int]()
    return String(x[Int])

# They have to be mutable for now, and implement Copyable & Movable
var an_int = IntOrString(4)
var a_string = IntOrString("I'm a string!")
var who_knows = IntOrString(0)
import random
if random.random_ui64(0, 1):
    who_knows.set[String]("I'm actually a string too!")

print(to_string(an_int))
print(to_string(a_string))
print(to_string(who_knows))

from utils import Variant
alias IntOrString = Variant[Int, String]
fn to_string(mut x: IntOrString) -> String:
    if x.isa[String]():
        return x[String]
    # x.isa[Int]()
    return String(x[Int])

# They have to be mutable for now, and implement Copyable & Movable
var an_int = IntOrString(4)
var a_string = IntOrString("I'm a string!")
var who_knows = IntOrString(0)
import random
if random.random_ui64(0, 1):
    who_knows.set[String]("I'm actually a string too!")

print(to_string(an_int))
print(to_string(a_string))
print(to_string(who_knows))

Parameters

• ​*Ts (Copyable & Movable): The elements of the variadic.

Implemented traits

AnyType, Copyable, ExplicitlyCopyable, Movable, UnknownDestructibility

Methods

__init__

__init__(out self, *, unsafe_uninitialized: Tuple[])

Unsafely create an uninitialized Variant.

Args:

• ​unsafe_uninitialized (Tuple): Marker argument indicating this initializer is unsafe.

@implicit __init__[T: Copyable & Movable](out self, var value: T)

Create a variant with one of the types.

Parameters:

• ​T (Copyable & Movable): The type to initialize the variant to. Generally this should be able to be inferred from the call type, eg. Variant[Int, String](4).

Args:

• ​value (T): The value to initialize the variant with.

__copyinit__

__copyinit__(out self, other: Self)

Creates a deep copy of an existing variant.

Args:

• ​other (Self): The variant to copy from.

__moveinit__

__moveinit__(out self, var other: Self)

Move initializer for the variant.

Args:

• ​other (Self): The variant to move.

__del__

__del__(var self)

Destroy the variant.

__getitem__

__getitem__[T: Copyable & Movable](ref self) -> ref [self] T

Get the value out of the variant as a type-checked type.

This explicitly check that your value is of that type! If you haven't verified the type correctness at runtime, the program will abort!

For now this has the limitations that it - requires the variant value to be mutable

Parameters:

• ​T (Copyable & Movable): The type of the value to get out.

Returns:

ref: A reference to the internal data.

copy

copy(self, out copy: Self)

Explicitly creates a deep copy of an existing variant.

Returns:

Self: A copy of the value.

take

take[T: Copyable & Movable](mut self) -> T

Take the current value of the variant with the provided type.

The caller takes ownership of the underlying value.

This explicitly check that your value is of that type! If you haven't verified the type correctness at runtime, the program will abort!

Parameters:

• ​T (Copyable & Movable): The type to take out.

Returns:

T: The underlying data to be taken out as an owned value.

unsafe_take

unsafe_take[T: Copyable & Movable](mut self) -> T

Unsafely take the current value of the variant with the provided type.

The caller takes ownership of the underlying value.

This doesn't explicitly check that your value is of that type! If you haven't verified the type correctness at runtime, you'll get a type that looks like your type, but has potentially unsafe and garbage member data.

Parameters:

• ​T (Copyable & Movable): The type to take out.

Returns:

T: The underlying data to be taken out as an owned value.

replace

replace[Tin: Copyable & Movable, Tout: Copyable & Movable](mut self, var value: Tin) -> Tout

Replace the current value of the variant with the provided type.

The caller takes ownership of the underlying value.

This explicitly check that your value is of that type! If you haven't verified the type correctness at runtime, the program will abort!

Parameters:

• ​Tin (Copyable & Movable): The type to put in.
• ​Tout (Copyable & Movable): The type to take out.

Args:

• ​value (Tin): The value to put in.

Returns:

Tout: The underlying data to be taken out as an owned value.

unsafe_replace

unsafe_replace[Tin: Copyable & Movable, Tout: Copyable & Movable](mut self, var value: Tin) -> Tout

Unsafely replace the current value of the variant with the provided type.

The caller takes ownership of the underlying value.

This doesn't explicitly check that your value is of that type! If you haven't verified the type correctness at runtime, you'll get a type that looks like your type, but has potentially unsafe and garbage member data.

Parameters:

• ​Tin (Copyable & Movable): The type to put in.
• ​Tout (Copyable & Movable): The type to take out.

Args:

• ​value (Tin): The value to put in.

Returns:

Tout: The underlying data to be taken out as an owned value.

set

set[T: Copyable & Movable](mut self, var value: T)

Set the variant value.

This will call the destructor on the old value, and update the variant's internal type and data to the new value.

Parameters:

• ​T (Copyable & Movable): The new variant type. Must be one of the Variant's type arguments.

Args:

• ​value (T): The new value to set the variant to.

isa

isa[T: Copyable & Movable](self) -> Bool

Check if the variant contains the required type.

Parameters:

• ​T (Copyable & Movable): The type to check.

Returns:

Bool: True if the variant contains the requested type.

unsafe_get

unsafe_get[T: Copyable & Movable](ref self) -> ref [self] T

Get the value out of the variant as a type-checked type.

This doesn't explicitly check that your value is of that type! If you haven't verified the type correctness at runtime, you'll get a type that looks like your type, but has potentially unsafe and garbage member data.

For now this has the limitations that it - requires the variant value to be mutable

Parameters:

• ​T (Copyable & Movable): The type of the value to get out.

Returns:

ref: The internal data represented as a Pointer[T].

is_type_supported

static is_type_supported[T: Copyable & Movable]() -> Bool

Check if a type can be used by the Variant.

Example:

from utils import Variant

def takes_variant(mut arg: Variant):
    if arg.is_type_supported[Float64]():
        arg = Float64(1.5)

def main():
    var x = Variant[Int, Float64](1)
    takes_variant(x)
    if x.isa[Float64]():
        print(x[Float64]) # 1.5

from utils import Variant

def takes_variant(mut arg: Variant):
    if arg.is_type_supported[Float64]():
        arg = Float64(1.5)

def main():
    var x = Variant[Int, Float64](1)
    takes_variant(x)
    if x.isa[Float64]():
        print(x[Float64]) # 1.5

For example, the Variant[Int, Bool] permits Int and Bool.

Parameters:

• ​T (Copyable & Movable): The type of the value to check support for.

Returns:

Bool: True if type T is supported by the Variant.

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