[ruby-core:95876] [Ruby master Feature#15563] #dig that throws an exception if an key doesn't exist

Issue #15563 has been updated by 3limin4t0r (Johan Wentholt).

Description updated

Changed naming from `#dig_e` to `#traverse`. Removed alternative options, and kept the strict version since `#fetch` is also strict. Possibility to expand upon this with a block or `:default` keyword argument is possible, but should be its own feature request.

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Feature #15563: #dig that throws an exception if an key doesn't exist
https://bugs.ruby-lang.org/issues/15563#change-82713

* Author: 3limin4t0r (Johan Wentholt)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
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Ruby 2.3.0 introduced `#dig` for *Array*, *Hash* and *Struct*. Both *Array* and *Hash* have `#fetch` which does the same as `#[]`, but instead of returning the default value an exception is raised (unless a second argument or block is given). *Hash* also has `#fetch_values` which does the same as `#values_at`, raising an exception if an key is missing. For `#dig` there is no such option.

My proposal is to add a method which does the same as `#dig`, but instead of using the `#[]` accessor it uses `#fetch`.

This method would look something like this:

```Ruby
module Traversable
  def traverse(key, *others)
    value = fetch(key)
    return value if others.empty?

    if value.respond_to?(__method__, true)
      value.send(__method__, *others)
    else
      raise TypeError, "#{value.class} does not have ##{__method__} method"
    end
  end
end

Array.include(Traversable)
Hash.include(Traversable)
```

The exception raised is taken from `#dig` (`[1].dig(0, 1) #=> TypeError: Integer does not have #dig method`).

```Ruby
yaml = YAML.load_file('some_file.yml')

# this change is meant to make chaining #fetch calls more easy
yaml.fetch('foo').fetch('bar').fetch('baz')

# would be replaced with
yaml.traverse('foo', 'bar', 'baz')
```

I'm curious to hear what you guys think about the idea as a whole, the method name and the two points described above.
 



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