Constants

Constants can be declared at the top level or inside other types. They must start with a capital letter:

PI = 3.14

module Earth
  RADIUS = 6_371_000
end

PI #=> 3.14
Earth::RADIUS #=> 6_371_000

Although not enforced by the compiler, constants are usually named with all capital letters and underscores to separate words.

A constant definition can invoke methods and have complex logic:

TEN = begin
  a = 0
  while a < 10
    a += 1
  end
  a
end

TEN #=> 10

If a constant is not used, its initializer is never included in the final executable.