object_rainbow/
enumkind.rs

1use crate::*;
2
3/// Discriminant arithmetic glue to make `#[derive(Enum)]` function.
4pub trait UsizeTag: Sized {
5    /// Used by [`EnumTag::from_const`].
6    ///
7    /// ## Panics
8    ///
9    /// Panics on out-of-bounds.
10    fn from_usize(n: usize) -> Self;
11    /// Convert a trusted value to [`usize`].
12    fn to_usize(&self) -> usize;
13    /// Convert an untrusted value to [`usize`].
14    fn try_to_usize(&self) -> Option<usize>;
15}
16
17/// [`EnumKind::Tag`].
18#[derive(
19    ToOutput, InlineOutput, ListHashes, Topological, Tagged, ParseAsInline, Size, MaybeHasNiche,
20)]
21pub struct EnumTag<T, const MAX: usize>(T);
22
23impl<T: UsizeTag, const MAX: usize> UsizeTag for EnumTag<T, MAX> {
24    fn from_usize(n: usize) -> Self {
25        assert!(n < MAX);
26        Self(UsizeTag::from_usize(n))
27    }
28
29    fn to_usize(&self) -> usize {
30        self.0.to_usize()
31    }
32
33    fn try_to_usize(&self) -> Option<usize> {
34        self.0.try_to_usize()
35    }
36}
37
38impl<T: UsizeTag, const MAX: usize> EnumTag<T, MAX> {
39    /// Inherent alias of [`UsizeTag::to_usize`].
40    pub fn to_usize(&self) -> usize {
41        self.0.to_usize()
42    }
43
44    /// Generate the tag from a statically known index.
45    pub fn from_const<const N: usize>() -> Self {
46        assert!(N < MAX);
47        Self(UsizeTag::from_usize(N))
48    }
49}
50
51impl<T: ParseInline<I> + UsizeTag, I: ParseInput, const MAX: usize> ParseInline<I>
52    for EnumTag<T, MAX>
53{
54    fn parse_inline(input: &mut I) -> crate::Result<Self> {
55        let n_raw = T::parse_inline(input)?;
56        let n: Option<usize> = n_raw.try_to_usize();
57        if let Some(n) = n
58            && n < MAX
59        {
60            return Ok(Self(n_raw));
61        }
62        Err(Error::DiscriminantOverflow)
63    }
64}
65
66/// An [`Inline`] identifying variants of an [`Enum`].
67pub trait EnumKind: Copy {
68    /// Underlying [`Inline`]. Typically [`EnumTag`].
69    type Tag;
70    /// Get the underlying [`Inline`].
71    fn to_tag(self) -> Self::Tag;
72    /// Convert from an [`EnumTag`] assuming the value is within bounds, such that otherwise we have
73    /// caught their violation during parsing of that tag.
74    ///
75    /// Panics on out-of-bounds.
76    fn from_tag(tag: Self::Tag) -> Self;
77}
78
79/// `enum`.
80pub trait Enum {
81    /// Discriminant uniquely identifying this `enum`'s variants.
82    type Kind: EnumKind;
83    /// Get the [`EnumKind`] of this variant.
84    fn kind(&self) -> Self::Kind;
85}
86
87/// [`Enum`]-specific [`Parse`].
88pub trait EnumParse<I: ParseInput>: Enum + Parse<I> {
89    /// Given an already-parsed [`EnumKind`], parse the rest of a [`Parse`] [`Enum`].
90    fn enum_parse(kind: Self::Kind, input: I) -> crate::Result<Self>;
91    /// For implementing [`Parse::parse`].
92    fn parse_as_enum(mut input: I) -> crate::Result<Self>
93    where
94        <Self::Kind as EnumKind>::Tag: ParseInline<I>,
95    {
96        Self::enum_parse(Self::Kind::from_tag(input.parse_inline()?), input)
97    }
98}
99
100/// [`Enum`]-specific [`ParseInline`].
101pub trait EnumParseInline<I: ParseInput>: Enum + ParseInline<I> {
102    /// Given an already-parsed [`EnumKind`], parse the rest of a [`ParseInline`] [`Enum`].
103    fn enum_parse_inline(kind: Self::Kind, input: &mut I) -> crate::Result<Self>;
104    /// For implementing [`ParseInline::parse_inline`].
105    fn parse_as_inline_enum(input: &mut I) -> crate::Result<Self>
106    where
107        <Self::Kind as EnumKind>::Tag: ParseInline<I>,
108    {
109        Self::enum_parse_inline(Self::Kind::from_tag(input.parse_inline()?), input)
110    }
111}
object_rainbow/enumkind.rs

object_rainbow/
enumkind.rs
