I'm fairly new to ruby and I'm a bit confused by what the map! syntax does. I see the following line on the codebase
b.map(&:values).uniq!.map!
b.map(&:values).uniq! gives me the following output:
[["us"],
["au"],
["fr"],
["mx"],
["ad",
"ae",
"af",
"al",
"am",
"ao",
"aq"]]
When I add a .map! to the end of b.map(&:values).uniq! I get #<Enumerator: ...>. I'm not really sure what is happening. If anyone could explain to me what is going on that would be very helpful.
From the documentation:
Invokes the given block once for each element of
self, replacing the element with the value returned by the block.See also
Enumerable#collect.If no block is given, an Enumerator is returned instead.
This means that if you have used map! with a block - the array would have replaced all its elements with the return value of the block:
b.map(&:values).uniq!.map!(&:first)
# => ["us", "au", "fr", "mx", "ad"]
Since you did not add a block, you got an Enumerator, which is like a delayed action cursor, where you can add your block later on:
enum = b.map(&:values).uniq!.map!
enum.each(&:first)
# => ["us", "au", "fr", "mx", "ad"]
