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What is a symbol in Ruby and when do I use one?

Ruby 2 min read Full lesson: Ruby For Loops and Iterators
Short answer

A symbol like :name is an immutable, interned identifier. Use symbols for hash keys, method names and option flags; use strings for text a user will read or edit.

ruby
:name.class      # Symbol
"name".class     # String

:name.object_id == :name.object_id      # true — the same object every time
"name".object_id == "name".object_id    # false — two separate strings

Every occurrence of :name in your program is the same object in memory. That makes symbol comparison a pointer check rather than a character-by-character one, which is why hashes use them.

#The rule of thumb

Symbol when it names something: hash keys, method names, states, option flags.

ruby
video = { title: "Intro to Ruby", track: :ruby, level: :beginner }
send(:upcase)
attr_accessor :name

String when it is content: anything displayed, stored, concatenated or edited.

#The modern hash syntax

ruby
{ title: "Intro" }           # symbol keys — the common form
{ :title => "Intro" }        # identical, older syntax
{ "title" => "Intro" }       # string keys — different keys entirely

hash[:title] and hash["title"] are not interchangeable. Mixing them is a frequent source of nil where you expected a value.

#Converting

ruby
:ruby.to_s      # "ruby"
"ruby".to_sym   # :ruby

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