Tracking Issue for `or_try_*` variants for `BTreeMap` and `HashMap` Entry API

Feature gate: #![feature(try_entry)]

This is a tracking issue for rust-langs/libs-team#336. It introduces a couple of or_try_* methods to HashMap/BTreeMap Entry API to make it ergonomic to use the Entry API in cases where the construction of a value fails.

Public API

// std::collections::btree_map::entry or std::collections::hash_map::entry

impl Entry<K, V> {
    pub fn or_try_insert_with<F: FnOnce() -> Result<V, E>, E>(
        self,
        default: F,
    ) -> Result<&'a mut V, E> { ... };

    pub fn or_try_insert_with_key<F: FnOnce(&K) -> Result<V, E>, E>(
        self,
        default: F,
    ) -> Result<&'a mut V, E> { ... };
}

Steps / History

(Remember to update the S-tracking-* label when checking boxes.)

• ACP: rust-lang/libs-team#336
• Implementation:
  • #120708 (HashMap's Entry or_try_* methods by peterjoel)
  • #157355
• Final comment period (FCP)^1
• Stabilization PR

Unresolved Questions

• None yet.

Start by reading the std::collections::btree_map::entry and std::collections::hash_map::entry API summary, then review implementation PRs #120708 and #157355. The issue is complete when unresolved questions are addressed and the remaining FCP and stabilization steps are completed.