Programming Crystal

Using Symbols as Identifiers

The strings you’ve been using in this chapter are flexible, but that flexibility imposes performance costs. Suppose you need to sift through a huge file with millions of mineral objects and give each their mineral name, essentially assigning an identifier. You’d be better off using Symbols here, because every instance of a given Symbol is exactly the same object:

types_and_control_flow/symbols.cr

class Mineral
  property name

  def initialize(@name : Symbol)
  end
end

mineral1 = Mineral.new(:talc)
mineral8547 = Mineral.new(:talc)

p mineral1.name
# => :talc
p mineral8547.name # => :talc
p :talc            # => :talc

mineral8547.name = :gold
:gold.class # => Symbol

Because ...