[ruby-core:119590] [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).


> I don’t think it can be treated as “explicitly”

The `**` is right there in the code, written out caller-side, you can't get more "explicit" than that.

> We can apply the same argument to `1 + obj`

No we can't; as you know `+` is a method (I guess that would make `**` a "true" operator?) so `1.+(obj)` is similar to `{}.merge(obj)` and falls under implicit conversion (which the method is free to do or not)

> What if it _is_ a typo/error?

Then I'll fix my stupid mistakes by my own stupid self, thank you very much.

> Now, if the user misuses it (by mistake or misunderstanding) and passes some, say, ActiveRecord model as a second parameter, then, with `to_h`, it would be successfully unpacked

I think that would be awesome. If I do `other_method(**model)` and that `model` is representable as a hash, passing it as keyword arguments is beautiful.
Imagine something like
```ruby
ValidOptions = Struct.new(:ssl, :host, :port)
opts = ValidOptions.new
opts.port = 999
setup_request(**opts)
```

> * problem of things being _unintentionally_ unpacked, considering how many objects have `to_h` method

That never happens. I have never ever written code where `foo(**opts)` throws "no implicit conversion of Object into Hash" and then I realize I really meant to use something other than `opts`.

> (other than `**(params if condition?)`, which was actually handled).

I'll admit that `**nil` covers 90% of the benefits, but the adhoc-ness of it all is a bit frustrating.


----------------------------------------
Feature #15381: Let double splat call `to_h` implicitly
https://bugs.ruby-lang.org/issues/15381#change-110211

* 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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