The Ruby Way: Solutions and Techniques in Ruby Programming, Second Edition

6.1. Symbols

A symbol in Ruby is an instance of the class Symbol. The syntax is simple in the typical case: a colon followed by an identifier.

A symbol is like a string in that it corresponds to a sequence of characters. It is unlike a string in that each symbol has only one instance (just as a Fixnum works). Therefore, there is a memory or performance issue to be aware of. For example, in the following code, the string "foo" is stored as three separate objects in memory, but the symbol :foo is stored as a single object (referenced more than once):

array = ["foo", "foo", "foo", :foo, :foo, :foo]

Some people are confused by the leading colon on a symbol name. There is no need for confusion; it’s a simple matter of syntax. Strings, arrays, and ...