From: "Dan0042 (Daniel DeLorme) via ruby-core" <ruby-core@...>
Date: 2024-10-22T18:10:03+00:00
Subject: [ruby-core:119588] [Ruby master Feature#15381] Let double splat call `to_h` implicitly

Issue #15381 has been updated by Dan0042 (Daniel DeLorme).


`to_{t}` methods are for explicit type conversion, and `to_{type}` methods are for implicit type conversion.

`{}.merge(obj)` => obj is implicitly expected to be Hash, or converted via #to_hash
`{}.merge(obj.to_h)` => obj is explicitly converted via #to_h
`{}.merge(**obj)` => obj is **explicitly** splatted but conversion is done via #to_hash instead of #to_h. It makes no sense, as many many people have commented through the years.

If you're double-splatting an object, of course you'd expect it to be convertible to a Hash. Please assume I'm not an idiot and that `**obj` is my intent, not a typo. Being overly restrictive (only true Hash-like objects can be used!) serves no purpose. Having to do `**obj.to_h` is silly, and adding #to_hash to a class in order to make it splattable is even more silly (possibly dangerous).

The fix is easy and backward-compatible; just let double splat convert the object with both #to_hash and #to_h. But instead the "fix" that we got is a weird (although useful) one-off exception for `**nil`. ����

----------------------------------------
Feature #15381: Let double splat call `to_h` implicitly
https://bugs.ruby-lang.org/issues/15381#change-110209

* Author: sawa (Tsuyoshi Sawada)
* Status: Open
----------------------------------------
The single splat calls `to_a` implicitly on the object (if it is not an array already) so that, for example, we have the convenience of writing conditions in an array literal:

```ruby
a = [
  *(:foo if some_condition),
  *(:bar if another_condition),
]
```

And the ampersand implicitly calls `to_proc` on the object (if it is not a proc already) so that we can substitute a block with an ampersand followed by a symbol:

```ruby
some_method(&:some_method_name)
```

Unlike the single splat and ampersand, the double splat does not seem to implicitly call a corresponding method. I propose that the double splat should call `to_h` implicitly on the object if it not already a Hash so that we can, for example, write a condition in a hash literal as follows:

```ruby
h = {
  **({a: 1} if some_condition),
  **({b: 2) if another_condition),
}
```

There may be some other benefits of this feature that I have not noticed yet.



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