TIL, 2017-12-01

Cons to using `fetch(:thingie)` vs `[:thingie]`?

If you use fetch, use the block form, not the default value form, because the block runs only when the key is missing, whereas the default value runs every time.
fetch if you want to produce an error if no key, or you want to specify a default value.
The problem with a['key'] is that you are assuming that a is always a hash. Strings also have the method [] but doesn’t have the method fetch so you can find errors easier.
fetch: Easier to debug KeyNotFound rather than letting a nil string trickle into your code and have to debug whatever that happens to cause.
You can also use Hash#dig and Array#dig over fetch.