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#![deny(missing_docs)]
//! This crate augments the `frunk` crate with extra functionallity to allow transmogrification
//! between enums with similar structures.
//!
//! This crate specifically defines the data structures used in the generic representation of an
//! enum, the `frunk-enum-derive` crate adds a proc-macro to auto-generate the per-type code needed
//! to take advantage of this core function.
use frunk::labelled::Transmogrifier;
use frunk::{HCons, HNil};
use std::marker::PhantomData;
/// A building block for a generic enum. The "additive-type" mirror for `frunk::HCons`. This is
/// normally used as:
///
/// ```ignore
/// HEither<A,
/// HEither<B,
/// HEither<C,
/// Void>>>
/// ```
pub enum HEither<H, T> {
/// The first variant.
Head(H),
/// The second/other variant.
Tail(T),
}
/// A generic representation of an enum variant. This holds the ident of the variant at both type
/// and value levels.
pub struct Variant<K, T> {
/// A text representation of the variant ident
pub key: &'static str,
/// The value of the contents of the variant
pub value: T,
/// A type-level representation of the variant ident
pub name_type_holder: PhantomData<K>,
}
/// A macro to ease the creation of `Variant`s. See `frunk::field!` for usage.
#[macro_export]
macro_rules! variant {
// No name provided and type is a tuple
(($($repeated: ty),*), $value: expr) => {
$crate::variant!( ($($repeated),*), $value, concat!( $(stringify!($repeated)),* ) )
};
// No name provided and type is a tuple, but with trailing commas
(($($repeated: ty,)*), $value: expr) => {
$crate::variant!( ($($repeated),*), $value )
};
// We are provided any type, with no stable name
($name_type: ty, $value: expr) => {
$crate::variant!( $name_type, $value, stringify!($name_type) )
};
// We are provided any type, with a stable name
($name_type: ty, $value: expr, $name: expr) => {
$crate::Variant::<$name_type,_> {
key: $name,
value: $value,
name_type_holder: std::marker::PhantomData,
}
}
}
impl<TargetHead, TargetTail, SourceHead, SourceTail, HeadIndices, TailIndices, Key>
Transmogrifier<HEither<Variant<Key, TargetHead>, TargetTail>, HCons<HeadIndices, TailIndices>>
for HEither<Variant<Key, SourceHead>, SourceTail>
where
SourceHead: Transmogrifier<TargetHead, HeadIndices>,
SourceTail: Transmogrifier<TargetTail, TailIndices>,
{
#[inline(always)]
fn transmogrify(self) -> HEither<Variant<Key, TargetHead>, TargetTail> {
match self {
HEither::Head(Variant {
value: h, key: k, ..
}) => HEither::Head(variant!(Key, h.transmogrify(), k)),
HEither::Tail(t) => HEither::Tail(t.transmogrify()),
}
}
}
/// An uninhabited type.
pub enum Void {}
impl Transmogrifier<Void, HNil> for Void {
fn transmogrify(self) -> Void {
match self {}
}
}