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Ruby Symbols

A symbol is a light name tag that starts with a colon. Programs use symbols as hash keys when the key is a fixed name.

A symbol as a name tag

The symbol :ready names one state of a program. p shows the colon, and puts prints the name without it.

status = :ready
p status
puts status

Symbol keys with the short form

In the short form, the key name comes first and a colon follows it. p shows each key with the colon in front.

person = { name: "Ana", age: 30 }
p person
puts person[:name]

Symbol keys with the rocket form

The rocket form writes the colon before the name and joins the pair with =>. It builds the same hash as the short form.

person = { :name => "Ana", :age => 30 }
p person
puts person[:age]

One symbol and two strings

equal? asks whether two things are the very same object. The symbol test gives true, the string test gives false, and the == test still matches the two texts.

puts :ready.equal?(:ready)
puts "ready".equal?("ready")
puts "ready" == "ready"

Example

order = { item: "book", count: 2 }
order[:count] = 5
p order
puts order[:item]
puts order.length

Key points

  • A symbol starts with a colon, like :ready.
  • A symbol is a name a program uses, not a piece of text it works on.
  • The same symbol written twice is the same single object.
  • Two strings with the same letters are two separate objects.
  • The == test compares values, so two strings with the same letters pass it.
  • A symbol key can be written as name: or as :name => in a hash.

In this example, the order hash uses symbol keys written in the short form. The value under count changes to 5, and p prints the whole hash. The last two lines read the item by its symbol key and count the pairs.

Note

Strings hold text that can change. Symbols hold names that stay fixed.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Programiz Ruby Compiler

Exercise

What does puts :ready.equal?(:ready) print?