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Showing content from https://github.com/rust-lang/rust/issues/82766 below:

Tracking Issue for map_try_insert · Issue #82766 · rust-lang/rust · GitHub

Feature gate: #![feature(map_try_insert)]

This is a tracking issue for BTreeMap::try_insert and HashMap::try_insert.

Unlike .insert(), .try_insert() does not overwrite existing values, and has a meaningful error type with more context. See #82764

// alloc::collections::btree_map

impl<K: Ord, V> BTreeMap<K, V> {
    pub fn try_insert(&mut self, key: K, value: V) -> Result<&mut V, OccupiedError<'_, K, V>>;
}

pub struct OccupiedError<'a, K: 'a, V: 'a> {
    pub entry: OccupiedEntry<'a, K, V>,
    pub value: V,
}

impl<K: Debug + Ord, V: Debug> Debug for OccupiedError<'_, K, V>;
impl<'a, K: Debug + Ord, V: Debug> Display for OccupiedError<'a, K, V>;
impl<'a, K: Debug + Ord, V: Debug> Error for OccupiedError<'a, K, V>;

// std::collections::hash_map

impl<K: Eq + Hash, V, S: BuildHasher> HashMap<K, V, S> {
    pub fn try_insert(&mut self, key: K, value: V) -> Result<&mut V, OccupiedError<'_, K, V>>;
}

pub struct OccupiedError<'a, K: 'a, V: 'a> {
    pub entry: OccupiedEntry<'a, K, V>,
    pub value: V,
}

impl<K: Debug, V: Debug> Debug for OccupiedError<'_, K, V>;
impl<'a, K: Debug, V: Debug> fmt::Display for OccupiedError<'a, K, V>;
impl<'a, K: Debug, V: Debug> Error for OccupiedError<'a, K, V>;

• Issue: Missing a good way to insert into a HashMap while panicking on duplicates rfcs#3092
• Implementation: Add {BTreeMap,HashMap}::try_insert #82764
• Final commenting period (FCP)
• Stabilization PR

• Should OccupiedError implement Error (and Display)? Add {BTreeMap,HashMap}::try_insert #82764 (comment)
• Should OccupiedError have public fields, or accessors? Add {BTreeMap,HashMap}::try_insert #82764 (comment)
• try_ might imply it returns an Err when allocating fails, which is not the case. Maybe rename it to insert_new or something?
• Put the key: K argument into the OccupiedError?

jkugelman, turbocool3r, elichai, finnbear, uros-5 and 7 morerMazeiks, ThrashAbaddon, ElijahVlasov, andrii0lomakin, ciffelia and 20 more

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