rust-lang / rust-lang/rfcs

Add HashMap.entry_or_clone() method

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Description

Sometimes I have a key type which implements Clone, but for efficiency reasons I don't want to clone it unless it's absolutely necessary.

In this case it would be nice to have a method

my_hash_map.entry_or_clone(&k)

which behaves identically to

my_hash_map.entry(k.clone())

but only bothers to clone k if the key doesn't already exist in my_hash_map.

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  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reviewing the proposed HashMap.entry_or_clone(&k) API alongside the existing entry(k.clone()) behavior. Define the method's expected result for existing and missing keys, then evaluate the API through the Rust RFC process; done means the proposal has a decided design and any required implementation scope is clear.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
backend-api-design
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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