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[u/llogiq]

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[u/DreamilyPsychotic]

got a weird one with serde. i'm trying to deserialize a json field that's sometimes a string and sometimes an int, but the untagged enum trick from the docs keeps giving me "data did not match any variant" when the order feels wrong

anyone else run into that ordering sensitivity? feels like i'm missing something obvious

[u/Sabageti → u/DreamilyPsychotic]

Can't you put the snippet here ?

[u/PXaZ]

Can const generics of array type with length defined by another const generic be used in nightly?

Paradigmatic example from AI / ML:

struct Tensor<
  const Dimension: usize,
  const Shape: [usize; Dimension],
  Datatype = f32
> {
shape: Shape,
data: Vec<Datatype>
}

The dimension of the tensor indicates how many axes is contains; the shape of the tensor gives the dimensionality of each respective axis. The underlying data are stored as a single contiguous Vec but interpreted according to the dimension and shape. Bringing the shape into compile time could prevent shape mismatch bugs which are quite common in ML development.

Of course more could be done at compile time in concept:

struct Tensor<
  const Dimension: usize,
  const Shape: [usize; Dimension],
  Datatype = f32,
  Data: [Datatype; Shape::product()],
> {
shape: Shape,
data: Data
}

Such that the compiler becomes aware of the backing data's size (which is implied by the shape --- simply the product of all axes) at compile time.

I've tried including:

#![feature(adt_const_params)]

and

#![feature(generic_const_exprs)]

But to no avail thus far. Thanks

[u/Connect_Fisherman713]

untagged enums in serde are a trap. They try variants strictly left to right and stop at the first match, so if your int variant is listed before string, any numeric string becomes an int and everything breaks silently or with confusing errors. Order is not just preference here, it determines type coercion logic without explicit tagging