symbolize_keys

Explanation

The provided Rails code initializes a hash h with two key-value pairs:

1. :key with a value of 42.
2. 'key' (a string) with a value of 84.

Then, the method symbolize_keys is invoked on the hash h.

This method is a Rails extension to the Hash class, which converts keys in the hash to symbols.

However, since there's already a key :key in the hash, the symbolize_keys method doesn't change it.

Instead, it converts the string key 'key' to a symbol :key.

So, after invoking symbolize_keys, the hash h effectively becomes:

{ :key => 42, :key => 84 }

Since duplicate keys are not allowed in a hash in Ruby, the value associated with the second occurrence of :key (which is 84) overwrites the previous value (42).

Thus, the final output of h.symbolize_keys is
{ key: 84 }.

Voilà!