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use crate::{EnumTable, Enumerable, intrinsics};
impl<K: Enumerable, V, const N: usize> EnumTable<K, V, N> {
/// Creates a new `EnumTable` from `pairs`, or returns `None` if `pairs` doesn't
/// contain exactly one entry for each variant of `K`.
///
/// # Examples
///
/// ```rust
/// use enum_table::{EnumTable, Enumerable};
///
/// #[derive(Enumerable, Copy, Clone, Debug, PartialEq)]
/// enum Color {
/// Red,
/// Green,
/// Blue,
/// }
///
/// let pairs = [
/// (Color::Red, "Red"),
/// (Color::Green, "Green"),
/// (Color::Blue, "Blue"),
/// ];
/// let table = EnumTable::<Color, &str, { Color::COUNT }>::checked_from_pairs(pairs).unwrap();
/// assert_eq!(table.get(Color::Red), &"Red");
/// assert_eq!(table.get(Color::Green), &"Green");
/// assert_eq!(table.get(Color::Blue), &"Blue");
/// ```
///
/// A duplicate entry is rejected, instead of silently producing a table with an
/// unrelated variant missing:
///
/// ```rust
/// use enum_table::{EnumTable, Enumerable};
///
/// #[derive(Enumerable, Copy, Clone, Debug, PartialEq)]
/// enum Color {
/// Red,
/// Green,
/// Blue,
/// }
///
/// let pairs = [
/// (Color::Red, "Red"),
/// (Color::Green, "Green"),
/// (Color::Red, "Duplicate Red"),
/// ];
/// assert_eq!(
/// EnumTable::<Color, &str, { Color::COUNT }>::checked_from_pairs(pairs),
/// None
/// );
/// ```
pub fn checked_from_pairs(
pairs: impl IntoIterator<Item = (K, V), IntoIter: ExactSizeIterator>,
) -> Option<Self> {
let pairs = pairs.into_iter();
if pairs.len() != N {
return None;
}
let mut slots: [Option<V>; N] = core::array::from_fn(|_| None);
for (key, value) in pairs {
let idx = key.variant_index();
if slots[idx].is_some() {
return None;
}
slots[idx] = Some(value);
}
let table = intrinsics::try_collect_array(|i| slots[i].take().ok_or(())).ok()?;
Some(Self::new(table))
}
}
#[cfg(test)]
mod tests {
use super::*;
#[derive(Debug, Clone, Copy, PartialEq, Eq, Enumerable)]
enum Color {
Red = 33,
Green = 11,
Blue = 222,
}
#[test]
fn checked_from_pairs() {
let pairs = [
(Color::Red, "Red"),
(Color::Green, "Green"),
(Color::Blue, "Blue"),
];
let table = EnumTable::<Color, &str, { Color::COUNT }>::checked_from_pairs(pairs).unwrap();
assert_eq!(table.get(Color::Red), &"Red");
assert_eq!(table.get(Color::Green), &"Green");
assert_eq!(table.get(Color::Blue), &"Blue");
}
#[test]
fn checked_from_pairs_wrong_len() {
let pairs = [(Color::Red, "Red"), (Color::Green, "Green")];
assert_eq!(
EnumTable::<Color, &str, { Color::COUNT }>::checked_from_pairs(pairs),
None
);
}
#[test]
fn checked_from_pairs_duplicate_key() {
let pairs = [
(Color::Red, "Red"),
(Color::Green, "Green"),
(Color::Red, "Duplicate Red"),
];
assert_eq!(
EnumTable::<Color, &str, { Color::COUNT }>::checked_from_pairs(pairs),
None
);
}
#[test]
fn checked_from_pairs_missing_variant() {
let pairs = [(Color::Red, "Red"), (Color::Green, "Green")];
// 2 pairs against N=3 is caught by the length check before the missing-variant
// path is ever reached, so exercise it via an iterator whose (inaccurate)
// `ExactSizeIterator::len` matches `N` but whose actual items still leave a
// variant unfilled.
struct LyingLen<I>(I, usize);
impl<I: Iterator> Iterator for LyingLen<I> {
type Item = I::Item;
fn next(&mut self) -> Option<Self::Item> {
self.0.next()
}
}
impl<I: Iterator> ExactSizeIterator for LyingLen<I> {
fn len(&self) -> usize {
self.1
}
}
let iter = LyingLen(pairs.into_iter(), 3);
assert_eq!(
EnumTable::<Color, &str, { Color::COUNT }>::checked_from_pairs(iter),
None
);
}
}