[ruby-core:119592] [Ruby master Feature#15381] Let double splat call `to_h` implicitly

["Dan0042 (Daniel DeLorme) via ruby-core" <ruby-core@ml.ruby-lang.org>]

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


> There are certainly backwards compatibility issues from changing `**` from calling `to_hash` to `to_h`.

What kind of backwards compatibility issues exactly? My idea was to call #to_hash and fall back to #to_h, that should ensure no backwards incompatibility at all, unless I'm missing something?

> Using the unary `**` operator on an object would call the `**@` method, which should return a hash (or raise an exception).

That's a very intriguing solution, and very elegant I have to say.

----------------------------------------
Feature #15381: Let double splat call `to_h` implicitly
https://bugs.ruby-lang.org/issues/15381#change-110213

* 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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