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identity_vs_equality_key_comparison

🆔 Identity vs. Equality in Hash Keys​

By default, hashes compare keys with eql? and hash. Use compare_by_identity to switch to object‐identity (equal?), which can be helpful for caching or memoization:

cache = {}.compare_by_identity
obj1 = "foo".freeze
obj2 = "foo".freeze

cache[obj1] = :from_obj1
puts cache[obj2]  #=> nil, because obj2 is a different object
puts cache[obj1]  #=> :from_obj1

Switching comparison strategy can prevent accidental collisions when you need to treat even eql? objects as distinct keys.