Issue #13583 has been updated by shyouhei (Shyouhei Urabe).


Thank you for issuing this.  I see there is an obvious needs for this transformation (stringify_keys) so I'm :+1: to the feature.

Let's have a concrete definition of this requested method:

- Its name is Hash#transform_keys.
- It returns a newly created Hash instance.
- It has zero arity.
- It yields,
    - with only one block parameter (which is a key of the original hash),
    - the evaluated value is the new key for the entry.
- When the new key conflicts, later entry silently discards former entry (see the description of this issue).

Is it okey? Am I missing something?  Do people have any opinion?

----------------------------------------
Feature #13583: Adding `Hash#transform_keys` method
https://bugs.ruby-lang.org/issues/13583#change-64971

* Author: graywolf (Gray Wolf)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
In 2.4, new useful method `Hash#transform_values` was added. I would like to propose also adding matching method `Hash#transform_keys`.

```ruby
{a: 1, b: 2}.transform_keys { |k| k.to_s }
=> {"a"=>1, "b"=>2}
```

What needs to be considered is what to do in case of two keys mapping to the same new key

```ruby
{ a: 1, b: 2 }.transform_keys {|_| :same_key } # what should happen?
```

I think using `Hash[]` as model behaviour is a good idea.

```ruby
Hash[{ a: 1, b: 2 }.map { |key, value| [:s, value] }]
=> {:s=>2}
```

it's also how `Hash#transform_keys` works in rails (afaict).

This is a follow up feature request to #9970, which seems to be stalled. If the behaviour can be agreed upon, I can try putting together a patch (if no one else wants to step up).



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