Setting a key in a map doesn't add the key if it isn't already there about aether HOT 2 CLOSED

Yes, to obey the lens laws suitably, there are two implementations, both of which maintain the logical "shape" of the data structure. So key_ will not modify a key that does not already exist. The alternative, value_ treats values as options, so a value which does not exist is None, which does exist is Some etc.

You'll often find that if you want to be adding values to a map, value_ is more useful and explicit.

from aether.

Fair. I'll let this rest here for other people's curiosity to be satisfied.

from aether.