[ruby-core:108682] [Ruby master Feature#14602] Version of dig that raises error if a key is not present

Issue #14602 has been updated by amcaplan (Ariel Caplan).


We can think of this as either a variation of `fetch` or a variation of `dig`. Ultimately it's both, of course, just depends how you look at it.

If we think of it as `fetch`-based, `deep_fetch` would be OK but we also might go with something that really describes quite literally what it does, which is `fetch` recursively. So, `fetch_recursive` or `rfetch` (think of `Array#bsearch` as prior art - though of course it's not 100% comparable) might be the way to go.

If we take the `dig`-based perspective, it's `dig` but non-permissive. So `dig_strict` might be the most literal way of explaining what it does.

Rather than advocating strongly for 1 specific word, I'd just gently recommend that we avoid introducing more dig-like verbs. While seasoned Rubyists will know the difference, newcomers won't have any obvious reason to assume that `dig` differs from `traverse` in strictness. At least there's a convention for `fetch` vs `[]` which already exists and we can use it to avoid introducing more new language/concepts.

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Feature #14602: Version of dig that raises error if a key is not present
https://bugs.ruby-lang.org/issues/14602#change-97723

* Author: amcaplan (Ariel Caplan)
* Status: Open
* Priority: Normal
----------------------------------------
Currently, if I have a hash like this:

~~~ ruby
{
    :name => {
        :first => "Ariel",
        :last => "Caplan"
    }
}
~~~

and I want to navigate confidently and raise a KeyError if something is missing, I can do:

~~~ ruby
hash.fetch(:name).fetch(:first)
~~~

Unfortunately, the length of the name, combined with the need to repeat the method name every time, means most programmers are more likely to do this:

~~~ ruby
hash[:name][:first]
~~~

which leads to many unexpected errors.

The Hash#dig method made it easy to access methods safely from a nested hash; I'd like to have something similar for access without error protection, and I'd think the most natural name would be Hash#dig!.  It would work like this:

~~~ ruby
hash = {
    :name => {
        :first => "Ariel",
        :last => "Caplan"
    }
}
hash.dig!(:name, :first) # => Ariel
hash.dig!(:name, :middle) # raises KeyError (key not found: :middle)
hash.dig!(:name, :first, :foo) # raises TypeError (String does not have #dig! method)
~~~




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