Macro ocaml_interop::ocaml_unpack_variant
source · macro_rules! ocaml_unpack_variant { ($self:ident => { $($($tag:ident)::+ $(($($slot_name:ident: $slot_typ:ty),+ $(,)?))? $(=> $conv:expr)?),+ $(,)? }) => { ... }; ($self:ident => { $($($tag:ident)::+ $({$($slot_name:ident: $slot_typ:ty),+ $(,)?})? $(=> $conv:expr)?),+ $(,)? }) => { ... }; }
Expand description
Unpacks an OCaml variant and maps it into a Rust enum.
This macro works on OCaml
<'gc, T>
values.
It is important that the order of the fields remains the same as in the OCaml type declaration.
§Note
Unlike with ocaml_unpack_record!
, the result of ocaml_unpack_variant!
is a Result
value.
An error will be returned in the case of an unexpected tag value. This may change in the future.
§Examples
enum Movement {
StepLeft,
StepRight,
Rotate(f64),
}
// Assuming an OCaml type declaration like:
//
// type movement =
// | StepLeft
// | StepRight
// | Rotate of float
//
// NOTE: What is important is the order of the tags, not their names.
let ocaml_variant_root = make_ocaml_movement(cr, &OCaml::unit());
let ocaml_variant = cr.get(&ocaml_variant_root);
let result = ocaml_unpack_variant! {
ocaml_variant => {
// Alternative: StepLeft => Movement::StepLeft
// <anyname> => <build-expr>
Movement::StepLeft,
Movement::StepRight,
// Tag field names are mandatory
Movement::Rotate(rotation: OCamlFloat),
}
}.unwrap();
// ...