[ruby-core:109853] [Ruby master Feature#19001] Data: Add #to_h symmetric to constructor with keyword args [Follow-on to #16122 Data: simple immutable value object]

["RubyBugs (A Nonymous)" <noreply@ruby-lang.org>]

Issue #19001 has been reported by RubyBugs (A Nonymous).

----------------------------------------
Feature #19001: Data: Add #to_h symmetric to constructor with keyword args  [Follow-on to #16122 Data: simple immutable value object]
https://bugs.ruby-lang.org/issues/19001

* Author: RubyBugs (A Nonymous)
* Status: Open
* Priority: Normal
----------------------------------------
*Extracted a follow-up to [#16122 Data: simple immutable value object](https://bugs.ruby-lang.org/issues/16122)*

# Proposal: Add a `#to_h` method symmetric to a constructor accepting keyword arguments

This allows round-trip between a `Hash` and a Value object instance, for example:

```ruby
Point = Data.define(:x, :y, :z)

points = [
  Point.new(x: 1, y: 0, z: 0),
  Point.new(x: 0, y: 1, z: 0),
  Point.new(x: 0, y: 0, z: 1),
]

hashes = points.map(&:to_h)

points_2 = hashes.map { |h| Point.new(**h) }

points_2 == points
#=> true
```

## Why?

Having symmetric operation between `#to_h` and a keyword-args constructor is a major ergonomic factor in usage of immutable value objects.

To play with code that works like this, you may take a look at the [Values gem](https://rubygems.org/gems/values)

## Alternatives

If there is no symmetric construction and de-construction along these lines, a number of use cases become more complicated and less ergonomic.



-- 
https://bugs.ruby-lang.org/