Abstract types serialization with `type` keys

[sairus7]

This example works only in one way - type key is lost trying to convert back to Dict:

abstract type Vehicle end
struct Car <: Vehicle; make::String; model::String; end
struct Truck <: Vehicle; make::String; model::String; payload::Float64; end

# Define how to choose concrete types based on source data
StructUtils.@choosetype Vehicle x -> x["type"] == "car" ? Car : Truck

# Now make can create the right type
car = StructUtils.make(Vehicle, Dict("type" => "car", "make" => "Toyota", "model" => "Corolla"))

StructUtils.make(Dict, car) # no type key

What is the recommended way to make type field working both ways?
Should we always define @nonstruct with custom lift/lower methods?

[quinnj]

The recommended two-way pattern in v2.8.3 is to keep @choosetype for inbound selection and define lower for the outbound representation. @nonstruct is not needed.

StructUtils.@choosetype Vehicle source ->
    source["type"] == "car" ? Car : Truck

StructUtils.lower(car::Car) =
    (; type="car", make=car.make, model=car.model)

StructUtils.lower(truck::Truck) =
    (; type="truck", make=truck.make, model=truck.model,
       payload=truck.payload)

Then both directions work:

encoded = StructUtils.make(Dict{String,Any}, car)
decoded = StructUtils.make(Vehicle, encoded)

For format-specific behavior, the same methods can take a custom StructStyle as their first argument.

I verified complete Car and Truck round trips on exact current main. Closing as answered.