What is the colon operator in Ruby?

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:foo is a symbol named “foo”. Symbols have the distinct feature that any two symbols named the same will be identical:

"foo".equal? "foo"  # false
:foo.equal? :foo    # true

This makes comparing two symbols really fast (since only a pointer comparison is involved, as opposed to comparing all the characters like you would in a string), plus you won’t have a zillion copies of the same symbol floating about.

Also, unlike strings, symbols are immutable.

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