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Map is an unordered collection of key-value pairs.
Zero value of a map is nil
.
Other languages call it a dictionary (C#, Python) or a hash table (C++).
Iteration over a map has a random order. Many languages are different in that respect.
Basics of maps:
https://codeeval.dev/gist/01d43f3ee1710c742ab352504c40b54f