Ruby hash equivalent to Python dict setdefault

Question

In Python it is possible to read a dictionary/hash key while at the same time setting the key to a default value if one does not already exist.

For example:

Answer 1

If you only want to modify the value returned by setdefault, you can express this via Hash#merge!:

Python:

>>> d = {}
>>> d.setdefault("k", []).append("v")
>>> d
{'k': ['v']}

Ruby:

[28] pry(main)> h = {}
=> {}
[29] pry(main)> h.merge!(k: [:v]) { |_key, old, new| old.concat(new) }
=> {:k=>[:v]}
[30] pry(main)> h
=> {:k=>[:v]}