Optional Tuple with Custom Structs throws Segmentation Error

[ghost]

I have a struct Scalar that should take in an integer value, and then optionally two more Scalars. Here's my current implementation:

from collections.optional import Optional


struct Scalar:
    var _children: Optional[Tuple[Scalar, Scalar]]

    fn __init__(
        inout self,
        _children: Optional[Tuple[Scalar, Scalar]],
    ) -> None:
        self._children = _children

If the contents of the Tuples were Ints, this works fine - but as soon as I change them to Scalars, Mojo crashes with a segmentation error, even though all types are valid.

How can I fix this, or is there some other way to implement this? Thanks in advance.

Edit:
See this reply for details.

[Brian-M-J]

Have a look at Optional. I don't think an empty tuple (()) would work with it but (None, None) would.

[ghost]

Thanks, that definitely helped. I was able to use something like this, which fixes my earlier issue:

from collections.optional import Optional


struct Scalar:
    var _children: Optional[Tuple[Scalar, Scalar]]

    fn __init__(
        inout self,
        _children: Optional[Tuple[Scalar, Scalar]],
    ) -> None:
        self._children = _children

While using Optional[Tuple[Scalar, Scalar]] works fine for the _children variable, when I change the __init__() parameter, however, Mojo crashes with a segmentation fault. How can I fix that? Thanks so much for helping.

[Brian-M-J]

I'm not a 100% sure what's going on, but in the docs for Optional it says:

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.

Your Scalar struct does not implement the CollectionElement trait, which may be what's causing the issue.

Try adding the @value decorator to the struct and make it inherit from CollectionElement as demonstrated here.

Edit: Also while looking through the Tuple docs:

The type of a literal tuple expression.

Since the Tuple type is meant for literal expressions, it may not be able to be stored in structs or variables. Try using a StaticTuple instead.

[ghost]

I tried playing around with it a bit, what I found was that the following worked:

from collections.optional import Optional


struct Scalar:
    var _children: Optional[Tuple[Int, Int]]

    fn __init__(
        inout self,
        _children: Optional[Tuple[Int, Int]],
    ) -> None:
        self._children = _children

But as soon as I changed from Ints to Scalars, Mojo threw a segmentation fault without any clear error message. As for the Optional type requiring a CollectionElement, that should have still worked because the Scalars are inside a Tuple - Tuple itself should be able to store any type.

I tried out the StaticTuple instead, but unfortunately since that doesn't have the CollectionElement trait I can't use it with Optional, so I'm kind of lost on what else I can do.

If you have any other ideas, they would be greatly appreciated - I've also been thinking of some other way I can implement this, but I don't know anything else (Scalar needs to take in an integer, and then optionally two other Scalars).

Thank you so much for all the help.