Modular•16mo ago•

1 reply

Is unpacking variadic arguments coming soon?

At the moment, variadic arguments can be passed to other functions via

VariadicList

VariadicList

and the like. However, this approach fails if the second function is more general. An example:

@value
@register_passable("trivial")
struct MyType(Stringable):
    fn __str__(self) -> String:
        return "MyType"

    fn do_stuff(self):
        pass

fn func2[T: Stringable](args: VariadicListMem[T]):
    for i in range(len(args)):
        print(str(args[i]))

fn func1(args: VariadicListMem[MyType]):
    for arg in args:
        arg[].do_stuff()
    func2(args)

fn func(*args: MyType):
    func1(args)

@value
@register_passable("trivial")
struct MyType(Stringable):
    fn __str__(self) -> String:
        return "MyType"

    fn do_stuff(self):
        pass

fn func2[T: Stringable](args: VariadicListMem[T]):
    for i in range(len(args)):
        print(str(args[i]))

fn func1(args: VariadicListMem[MyType]):
    for arg in args:
        arg[].do_stuff()
    func2(args)

fn func(*args: MyType):
    func1(args)

Here,

args

args

is a

VariadicList

VariadicList

and cannot be passed as

VariadicListMem

VariadicListMem

. Using

VariadicListMem

VariadicListMem

func2

func2

does not work, however, since

Stringable

Stringable

is not register passable. Making a register passable

Stringable

Stringable

trait, in turn, is not possible, because

AnyTrivialRegType

AnyTrivialRegType

is not trait and cannot be inherited from.

I run into a similar issue if I use the (actually preferred) version that is fully parametric:

trait MyTypeTrait(Stringable):
    fn do_stuff(self):
        ...

@value
struct MyType(MyTypeTrait):
    fn __str__(self) -> String:
        return "MyType"

    fn do_stuff(self):
        pass

fn func2[*Ts: Stringable](args: VariadicPack[_, Stringable, *Ts]):
    @parameter
    for i in range(args.__len__()):
        print(str(args[i]))

fn func1[*Ts: MyTypeTrait](args: VariadicPack[_, MyTypeTrait, *Ts]):
    @parameter
    for i in range(args.__len__()):
        args[i].do_stuff()
    func2(args)

fn func[*Ts: MyTypeTrait](*args: *Ts):
    func1(args)

fn main():
    func(MyType(), MyType())

trait MyTypeTrait(Stringable):
    fn do_stuff(self):
        ...

@value
struct MyType(MyTypeTrait):
    fn __str__(self) -> String:
        return "MyType"

    fn do_stuff(self):
        pass

fn func2[*Ts: Stringable](args: VariadicPack[_, Stringable, *Ts]):
    @parameter
    for i in range(args.__len__()):
        print(str(args[i]))

fn func1[*Ts: MyTypeTrait](args: VariadicPack[_, MyTypeTrait, *Ts]):
    @parameter
    for i in range(args.__len__()):
        args[i].do_stuff()
    func2(args)

fn func[*Ts: MyTypeTrait](*args: *Ts):
    func1(args)

fn main():
    func(MyType(), MyType())

Here, the general function cannot take the more specific variadic pack.

I understand if everyone is tired of the "when will XY be implemented" questions. However, for me the question is whether I have to build a big workaround (if it takes longer) or simply use duplicate code (if this can be fixed soon).

Any advice (or alternative solutions)?

Modular•16mo ago•

1 reply

samufi🌳

Is unpacking variadic arguments coming soon?

At the moment, variadic arguments can be passed to other functions via

VariadicList

VariadicList

and the like. However, this approach fails if the second function is more general. An example:

@value
@register_passable("trivial")
struct MyType(Stringable):
    fn __str__(self) -> String:
        return "MyType"

    fn do_stuff(self):
        pass

fn func2[T: Stringable](args: VariadicListMem[T]):
    for i in range(len(args)):
        print(str(args[i]))

fn func1(args: VariadicListMem[MyType]):
    for arg in args:
        arg[].do_stuff()
    func2(args)

fn func(*args: MyType):
    func1(args)

@value
@register_passable("trivial")
struct MyType(Stringable):
    fn __str__(self) -> String:
        return "MyType"

    fn do_stuff(self):
        pass

fn func2[T: Stringable](args: VariadicListMem[T]):
    for i in range(len(args)):
        print(str(args[i]))

fn func1(args: VariadicListMem[MyType]):
    for arg in args:
        arg[].do_stuff()
    func2(args)

fn func(*args: MyType):
    func1(args)

Here,

args

args

is a

VariadicList

VariadicList

and cannot be passed as

VariadicListMem

VariadicListMem

. Using

VariadicListMem

VariadicListMem

func2

func2

does not work, however, since

Stringable

Stringable

is not register passable. Making a register passable

Stringable

Stringable

trait, in turn, is not possible, because

AnyTrivialRegType

AnyTrivialRegType

is not trait and cannot be inherited from.

I run into a similar issue if I use the (actually preferred) version that is fully parametric:

trait MyTypeTrait(Stringable):
    fn do_stuff(self):
        ...

@value
struct MyType(MyTypeTrait):
    fn __str__(self) -> String:
        return "MyType"

    fn do_stuff(self):
        pass

fn func2[*Ts: Stringable](args: VariadicPack[_, Stringable, *Ts]):
    @parameter
    for i in range(args.__len__()):
        print(str(args[i]))

fn func1[*Ts: MyTypeTrait](args: VariadicPack[_, MyTypeTrait, *Ts]):
    @parameter
    for i in range(args.__len__()):
        args[i].do_stuff()
    func2(args)

fn func[*Ts: MyTypeTrait](*args: *Ts):
    func1(args)

fn main():
    func(MyType(), MyType())

trait MyTypeTrait(Stringable):
    fn do_stuff(self):
        ...

@value
struct MyType(MyTypeTrait):
    fn __str__(self) -> String:
        return "MyType"

    fn do_stuff(self):
        pass

fn func2[*Ts: Stringable](args: VariadicPack[_, Stringable, *Ts]):
    @parameter
    for i in range(args.__len__()):
        print(str(args[i]))

fn func1[*Ts: MyTypeTrait](args: VariadicPack[_, MyTypeTrait, *Ts]):
    @parameter
    for i in range(args.__len__()):
        args[i].do_stuff()
    func2(args)

fn func[*Ts: MyTypeTrait](*args: *Ts):
    func1(args)

fn main():
    func(MyType(), MyType())

Is unpacking variadic arguments coming soon?

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